LIBRARY OF CONGRESS. 

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UNITED STATES OF AMERICA. 



FIRST BOOK 



PHYSIOLOGY. 



FOR THE USE OF SCHOOLS. 



AN INTRODUCTION TO^THE LARGER WORK BY THE 
SAME AUTHOR. 



'/^o^' 



BY . 



X 



WORTHINGTON HOOKER, M. D., 

LATE PROFESSOR IN YALE COLLEGE. 



ILLUSTRATED BY ENSf^lN^'^'^khf^^^ 

^ m 27188a/ 



vCV>„ 



SHELDON AND dt)MPANY 

NEW YORK AND CHICAGO. 



DR. HOOKER'S PHYSIOLOGIES. 



A FIRST BOOK IN PHYSIOLOGY. 
HOOKER'S NEW PHYSIOLOGY. 



SHELDON & CO.'S MODERN SCHOOL READERS, 
IN FIVE BOOKS. 

OLNEY'S ARITHMETICS. 
PATTERSON'S SPELLERS. 
COLTON'S GEOGRAPHIES. 
AVERY'S NATURAL PHILOSOPHY. 
AVERY'S CHEMISTRY. 
HILL'S RHETORICS. 
BULLIONS' GRAMMARS. 



Copyright, 1855-1883, by W. Hooker. 



Manufactured by CASE, LOCKWOOD & BRAINARD CO. 




^l^ J ^l^ ^1^ ^i^ 



This book is intended for legiimers in the study of 
Physiology, of whatever age they may be. It is a " First 
Book '' for the adult as well as for the child. There is 
more in common between young and adult minds, in 
regard to a subject which is new to them, than is com- 
monly supposed. There is for both the same need of 
simple, clear, and precise statement, with familiar illus- 
tration. A book intended to instruct a child in any 
science should be so written, that it will be just as 
instructiye to an adult unacquainted with the subject. 
Not only so, but it should be so written, that it will 
interest and please a mind that has a full knowledge of 
the subject, by its logical and clear development of 
simple fundamental facts and principles. 

It is a common error to suppose, that there need not 
to be as logical a presentation of a subject in teaching 
children as in teaching adults. A correct logic, in the 
true sense of that word, is necessary in either case. In 
teaching any science, no matter what the age of the 
scholar may be, a natural, that is, a logical, arrange- 
ment of the facts and principles, is essential to success. 
Indeed, it is more essential at the outset than it is sub- 



IV PREFACE. 



seqiiently^ for the beginner lays the very foundations 
of his knowledge, upon which in his course of learning 
afterwards he builds up the superstructure. It is the 
simple facts and principles of science, such as should be 
taught to the beginner, that 2iVQ fundamental. In order 
that he may begin right, he must acquire a clear idea 
of these. This, it is obvious, cannot be done by a loose, 
partial, and ill-arranged presentation of them, but only 
by a presentation that is strictly logical. Commonly, 
this foundation-work, as it may be termed, has to be 
done over and over again, bringing much unnecessary 
labor to both teacher and scholar, simply because it is 
not done right at the outset. 

There is another consideration bearing upon this 
point, w^hich is of great importance. It is essential to 
the successful study of science that good habits of mind 
be formed, and the earlier they are formed the better. 
I need not stop to show that clear logical presentations 
of facts and principles tend to form such habits, and 
that a loose, confused mode of presenting them tends 
to form habits of an opposite character. 

Let me not be understood to advocate that promi- 
nence of logical framework, as it may be called, which 
is so common in books for instruction. With all this 
show of logical arrangement, there is often much that 
is really very illogical. With the beginner, at least, the 
less there is of the formalities of arrangement the better. 
And yet there should in reality be a strict regard to the 
proper logical order in introducing facts and principles 



PREFACE, 



to the mind of the learner. If this natural order be 
observed, every page that the student learns serves to 
prepare his mind for what comes after. There is no 
point in which books for instruction so often fail as 
in this. 

Most books for the instruction of beginners in science, 
present a strange mixture of child's talk, and language 
that the child cannot understand, but can only learn by 
rote. Even the hard technical terms of science often 
enter abundantly into the comjDound. It seems to be 
forgotten that great simplicity of language may ie the 
vehicle of even a deep philosophy, and is consistent ivith 
an elevated style. Clear, precise statement, logical order 
of arrangement, and felicitous illustration, are the ele- 
ments of such a style. And these elements cannot 
exist, unless there be an appreciation in the writer's 
mind of the attitude of the minds that he addresses. 
He naust not only see clearly the facts and principles of 
science himself, but he must know how to make others 
see them clearly also. 

It is obvious that in a " First Book " there must be 
a less number of points introduced than in a book 
intended for instruction afterward. The field of vision 
should be gradually enlarged as the learner advances. 
At first there must be a selection of such points as he 
can most readily understand, reserving the more difii- 
cult ones for another book. And while the second book 
should be much more ^complete than that which is 
designed for beginners, yet in the latter the really essen- 



VI PREFACE. 



tial and fundamental parts of the science should be 
clearly presented. 

The principles thus advanced I have endeavored to 
follow in the construction of this httle work. It is 
intended principally for the use of common schools, 
and yet, like my larger work on Physiology, it is 
adapted for general reading. It will prepare the reader 
and the scholar for the more full examination of the 
subject in the larger work. 

I need hardly say, that in order to teach from this 
book satisfactorily, it is necessary for the teacher to 
read both books. By doing so, he will see clearly in 
every case the reason of the selection that I have made 
in this work from the facts that are presented so fully 
in the other, and will therefore be better prepared to 
teach according to the plan that I have in view. The 
questions that I have placed at the bottom of each page 
can be altered as the teacher thinks best, to suit the 
different capacities of his scholars. For certain general 
directions in teaching Physiology, I refer him to the 
Appendix of my larger work. 




CHAPTER I. 

PAGE 

THE MACHINERY OF THE BODY 9 

CHAPTER II. 
THE DIFFERENT STRUCTURES OF THE BODY... 14 

CHAPTER III. 
DIGESTION 22 

CHAPTER IV. 
CIRCULATION OF THE BLOOD 36 

CHAPTER V. 
RESPIRATION 54 

CHAPTER VI. 
BUILDING AND REPAIRING..., 74 

CHAPTER VII. 
THE NERVOUS SYSTEM 94 



vni CONTENTS. 



CHAPTER VIM, 



PAGE 



THE BONES 107 

CHAPTER IX. 
THE MUSCLES 130 

CHAPTER X. 
THE EYE 153 

CHAPTER XI. 
THE EAR 168 

CHAPTER XII. 
CONNECTION OF THE MIND AND BODY 180 



FIRST BOOK IN PHYSIOLOGY. 



CHAPTER 1. 
THE MACHINERY OF THE BODT. 

1. When you look at any machine made by ma/i, 
you inquire what it is intended to do. You find, com- 
monly, that it is for some one purpose. Thus, a nail- 
machine makes nails, and does nothing else ; a paper- 
machine makes paper ; a locomotive draws cars on a 
track ; and so of other machines. 

2. But the human body is not a single machine for 
a single purpose. It is a complicated machine, and 
serves many purposes. It differs very much in this re- 
spect from the machines that man makes. While for 
example, it is a machine that walks, walking is not the 
only thing that it does. It is not like the locomotive, 
that does nothing but draw cars. It can perform a 
great variety of motions besides w^alking. It can run, 
jump, leap, climb, &c. 

3. You see the same difference, if instead of look- 
ing at the body as a whole, you look at any particular 
part of it. Look, for example, at the hand, and com- 

Wliat is said of machines made bv man? How does the machinerv 
of the body differ from these « 
1* 



10 FIRST BOOK IN PHYSIOLOGY. 

pare it with the most ingenious machinery that man 
has ever made. The variety of things that it can do 
is almost endless. So, too, if you open your moutli 
before a looking-glass, and move about that busy little 
machine, the tongue, you will get some idea of the 
great variety of motion that it can perform. 

4. But besides being a locomotive machine, capable 
of all this variety of motion, the human body is also 
a machine in which many things are made. Blood is 
made in it. This red fluid is made out of the food 
which this machine puts into its mouth and eats. And 
then from the blood are made all the various parts of 
the body. 

5. In order that the blood may be used to construct 
all parts of the body, it must be carried everywhere. 
Th^re is a wonderful set of machinery to do this. The 
heart is pumping night and day, sending out the 
blood through the pipes that branch out from it all 
over the body. 

6. Then the blood, when it has been used, is not fit 
to be us'bd again until it is changed. There is, there- 
fore, a set of machinery in the chest for the purpose 
of changing the blood. The blood is carried to the 
lungs, and there it is exposed to the air that we breathe 
into the lungs every time that we draw a breath. By 
being aired in this way, it is fitted to be used again, 
and it goes back to the heart that it may be pumped 
out again all over the body. 

7. But the most wonderful machinery in the body 

Mention some particular parts of the body in which this difference ia 
seen. What is made by the machinery of the body ? By what ma- 
ehineiy is the blood circulated ? How is the blood changed after it hw 
been .»ced ? 



MACHINERY OF THE BODY. H 

ij8 that which we find in the nervous system. The 
brain is the great central organ of this system. From 
it branch out white cords, called nerves, which are 
found in every part of the body. This nervous system 
is somewhat like a telegraph, though it is much more 
perfect and mysterious. The brain may be consid- 
ered as the central office, where the mind has its seat. 
The nerves may be called the wires, by which mes- 
sages are sent forth and received by the mind. 

8. Messages are sent by means of the nerves tu the 
muscles, whenever the mind wills that any part of the 
body move. Thus, when you wish to move your 
hand, messages are sent from the brain to the muscles 
that move this part. When the mind wills that the 
whole body shall move, a great number of these mes- 
sages are sent in all directions at once. 

9. The mind too receives messages through the 
nerves. It receives them from the senses. When 
we see, something is sent by means of the nerves of 
the eyes to the brain, and thus reaches the mind, just 
as electricity goes along the w^ires of a telegraph. And 
the same may be said of the other senses. 

10. Observe now how great a variety of machinery 
there is in the body. The digestive machinery grinds 
up the food with its teeth and mixes it with juices in 
such a way that blood is made out of it. Then the 
machinery of the circulation moves the blood about 
everywhere in the body, so that all the parts may be 
made out of it and be kept in repair. The breathing 

What is the most wondeiful machinery in the body? What is it 
•ike ? And how ? Describe what is done when the muscles act. How 
ind from what does the mind receive messages? Give what is stated 
11 ^ 10 about the variety of the machinery in the b^odv 



12 FIRST BOOK IN PHYSIOLOGY. 

machinery continually purifies the blood after it hag 
been used, and so fits it again for use. Then by meana 
of the nervous machinery the mind uses the parts that 
are thus constructed from the blood — viz., the mus- 
cles, the b )nes, and the organs of the senses. 

11. You see that some of the machinery of the 
body is for the purpose of making other machinery. 
This is the business of the machinery of the digestion, 
the circulation, and the respiration. This machinery 
makes nerves, and muscles, and bones, and the brain, 
and the eye, and the other organs of the senses. The 
object then of eating and drinking and breathing and 
having the blood circulate, is to make machinery for 
the mind to use. 

12. There is one difference between the machinery 
of the body and the machines constructed by man, that 
I have not yet mentioned. When man makes a ma- 
chine he cannot use it till it is completed. If he 
wishes to alter it or repair it, he cannot use it at all 
while he is doing this. But the machinery of the 
body is constantly altered while it is in use. I will 
illustrate this difference. 

13. The machinery of the child's body is small ma 
chinery, but every part of it gradually becomes larger, 
d,nd in manhood it is of its full size. But no machine 
made by man can grow to be a larger one. Now, tlie 
machmery of the body not only grows, but it is kept 
in use while it Is growing. A small telescope never 
grows to be a large one, but the little eye of the infant 



Cai; tbe nifichineiy that man makes be kept in use while he is altering 
or repairiug it? How is it "with the machinery of tbe body ? What is 
Raid of th ^. growing ol tlie machiuery of the body f 



MACHINERY OF THE BODY. IS 

grows to be the large eye of a man, and is used every 
day while this is done. A cord does not grow to be a 
rope, but the muscles grow as we use them. 

14. The machines that man constructs cannot be 
repaired while they are in use ; they have to lie hy jor 
repair^ as it is expressed. It is not so with the ma- 
chinery of the body ; repairing is going on while it is 
in use. In the machinery made by man it is doT'e 
only now and then, but in the machinery of the body 
it is done all the time, every day, every hour, ovovy 
moment. 

15. One thing is to be noticed, however, abor.l ^his 
repairing of the body. Some of its machinery must 
have seasons of rest, in order that the repair ir.^; may 
be thoroughly done. This is the case with the brain, 
the nerves, and the muscles. When the mind has 
worked these parts of the machinery during the day, 
the rest of night is needed to repair fully the wear 
and tear. Though the business of repairing them is 
going on all the time, more of it is done while they 
are at rest in the hours of s^.eep than when we are 
awake. 

16. Another thing to bo remarked is, that when the 
machinery is much deranged by disease, more rest 
dran is commonly taken at night is needed. There 
must be some lying by for repair now. Thus, if a 
*.iinb be inflamed, it must be kept still. An inflamed 
e3^e needs to have the light shut out from it. If the 
brain be diseased, the mind must be kept from using 

Does the machinery of the body he by for repair \ W^hat parts of 
rhe maehiuery of the body must have seasons of i-est to have the v%- 
pairing well done? What is ^a'A of the need of rest foi* repairing ii» 
'Jl^asp * 



14 FIRST BOOK IN PHYSIOLOGY. 



it as u nch as it possible ; that is, it must be kept from 
thinkiLg. And what is true of particular parts of the 
raacliinery is true of it as a whole. When the whole 
body is disordered, as in fever, all the machinery 
must be kept as quiet as possible. 

17. There is some of the machinery that never stops, 
either when we are sick or when we are asleep ; it 
is the breathing and the circulating machinery. The 
heart is always beating, and the chest is always heav- 
ing ; they never rest from their work, and they are 
stopped only by death. 

IS. In this chapter I have given you some genera* 
views of tlie machinery of the body. In the follow- 
ing chapters I shall describe particular parts of it, and 
shall explain to you how they operate. I shall speak 
of the machinery of digestion, of circulation, of respi- 
ration, the nervous machinery, &c., each of them 
separately. 



CH AFTER il. 

THE DIFFERENT STRUCTURES OF THE BODY. 

1. Before considering each subject particular!)/ 
let us look in this chapter at some of the various 
things or structures that make up the machinery of 
the body. By doing this, these subjects will be more 
clear to you. For, as I shall mention different parts 
of the body, as I proceed, you will understand me 
better, if you have some knowledge of these parts at 
the beginning. 

What parts of the machinery of the body never rest? 



DIFFERENT STKUCTURES OF THE BODY. U 



2. Notice first, the hard bones which are the frame- 
work of the body. These are very difi*erent in their 
shapes in different parts of the frame. For example^ 
in the leg and arm they are long and slender, while 
in the head they make a box to hold the brain. They 
rary much in size also. 

3. The bones are composed partly of mineral ana 
partly of animal substance. When you see a pile of 
bones near a slaughter-house, which have been a long 
time exposed to the air, you see only the mineral part 
of them. The animal or soft part has been taken 
away by the heat of the sun and the washing of the 
rain. The same thing can be done, very quickly, by 
exposing a bone to a very hot fire. A bone thus 
deprived of its animal part 
is very brittle, and breaks 
easily. 

4. The animal part of a 
bone can be obtained also i 
separate from the mineral 
part. This can be done by 
putting it into a mixture of 
an acid, called muriatic acid, 
and water. The acid takes 
the mineral part away, and 

Jeaves the animal part in per- 

"fect shape. While the mine- 
ral part is brittle, this soft 
animal part can be bent so as 

What is said of the shapes of the bones, aud of their size? Of whal 
two parts is bone composed ? How can the mineral part be obtained 
separate from the other part ? How can the animal part be obtainea 
oy itself^ 




10 FIKST BOOK IN PUVSIOLOGY. 

to be tied into a knot, if the bone be one of the long 
ones. Fig. 1 represents a thigh-bone thus tied, after 
being dej^rived of its mineral part. 

5. In the child, when the bones are growing, they 
do not have as much of the mineral part as the bones 
of old persons do. It is well that they do not ; fur if 
they did, the frequent falls of the child would often 
give him a broken bone. If an old person should 
have as many falls as children commonly do, his brit- 
tle boneo would very often snap asunder. A fall 
down stairs^ which in the child is generally followed 
only by a momentary fright, a short crying-spell, and 
perhaps a bruise, is apt to break some bone in the 
old, and may even destroy life. 

6. The bones are bound together by firm ligaments^ 
so that while they move on each other at the joints, 
.they are held in their places. The bones are moved 
by muscles. The muscles make up the bulk of the 
fleshy part of the body. Their color is red. The 
tendons are Avhite and shining cords, by which the 
muscles pull the bones, in moving them. 

7. As I must refer occasionally to the action of 
muscles before I come to the chapter on the muscles, 
I will explain to you now the manner in which they 
act. A muscle is composed of a great number of 
very small fibres or threads. When it acts, each one 
of these fibres shortens itself. 

What is the difFereoce between tlie bones of the old an'^ those of the 
^oung in regard to these two parts ? What would happen to the child 
if there \\ere not this diffei ence ? By what are the bones bound 
together ? By what are Ihey moved ' What are the Vondons ? Whal 
b a muscle composed of? 



DIFFERENT STRUCTURES OF THE BODY. J"? 



Fig. 2 



a 



a 



h 



Fig. 3. 



8. I will show how this 
shortening of the fibres moves 
the bones, by means of some 
figures. Suppose a^ in Fig. 
2, is a bone that is fixed so 
that it cannot be moved, and 
that h can be moved. Let c 
be a fibre that extends from 
the one bone to the other. If 
the fibre c shorten itself, it will 
draw the bone h towards <z, as 
represented in the lower figure. 
The same thing is true of a 
number of fibres, as represented 
in Fig. 3. You see, then, how 
it is true of a multitude of fibres, 
as they are bound together in a 
muscle. 

9. Let 6?, in Fig. 4, represent a 
bone that is fixed, and e a bone 
that moves on ^, with a hinge-like 
joint. If the fibres are relaxed, 
the bone e will be as in Fig. 4 ; 
but if the fibres contract, the bone 
will be as in Fig. 5. These two 
figures show the action of the lower jaw, as it la 
moved up and down by the muscles, in eating. In 
Fig. 4, e is like the lower jaw when it is down ; and 
in Fig. 5 it is like it when it is up, so that its teeth 
press against those of the fixed upper jaw. 



r- 


FiGs. 4, 5. 




( 


i^ 


::> 


"n- 


iiiiiiii 







Explain by figures 2 and S, how the fibres of a muscle act. IHu* 
erate the manner in which the muscles move the lower jaw in eating. 



18 FIRST BOOK IN PHYSIOLOGY. 



^'^^- ^' '^' 10. Figs. 6 and 7 show you 

— — f^aa how the muscle that benda 

^ the elbow acts. In Fig. 6 the 

bones a and i are represented 
as they are when the arm is 
extended out straight. The 
muscle w^hich is represented 
by the line c, is relaxed. 



When it contracts or shortens itself, the bone b wiU 
be bent upon a^ as seen in Fig. 7. 

11. These two examples of muscular action will be 
sufficient for the present. In some of the succeeding 
chapters you will see examples of other ways in 
which the muscles operate ; and, in the chapter on 
the muscles, the many various ways in which they 
act will be fully illustrated. 

12. I have thus spoken of the bones with their lig- 
ameiitSy and the muscles with their tendons. The 
limbs of the body are made up of these four struc- 
tures. They compose also all the outer parts or walls 
of the trunk of the body and of the head. Within 
these walls are the three great cavities of the body, 
containing its most important organs. 

13. In the cavity of the head is the brain. This 
delicate and soft organ is shut in very securely by 
that round box of bones, called the cranium or skull. 
The cavity of the chest contains the heart and the 
lungs. The walls of this cavity are the spinal column, 
or back-bone, as it called, the ribs, ^and the breast- 



illustrate the manner in which the muscles bend the arm at the 
elbow. Of what four structures are the limbs of the body composed ? 
What other parts d ) they compose ? 



DIFFERENT STRUCTURES OF THE BODY !« 

bone. These are strongly bound together by muscles 
and ligaments. In the cavity of the abdomen are the 
stomach, liver, &c. Its walls are the spine behind, 
and at the sides and in front, broad flat muscles and 
tendons. The organs contained in these three cavi- 
ties I shall speak of in other parts of this book. 

14. In all the different structures of the body of 
which I have spoken, there are blood-vessels, large 
and small, circulating the blood everywhere. Nerves 
too go everywhere, branching out from the brain and 
spinal marrow. They are whitish cords, which by 
dividing continually are distributed to all parts of the 
body. The blood-vessels and nerves are everywhere 
mingled together. For if you prick any part, the 
nerves feel the pain, and the blood-vessels at the same 
time let out their blood. 

15. All the parts and organs of the body are well 
packed together. They are so arranged that there is 
no loss of room. And there is a kind of packing 
material made use of everywhere between all the 
parts. It is a very fine and nice material. Tou can 
see it if you look at a piece of meat from any animal. 
If you pull the fibres of the meat a little apart, you 
will see a delicate white substance between them. 
You will also see different portions of the meat sepa- 
rated from each other by considerable layers of this 
substance. These are the different muscles with the 
packing material between them. 

16. This packing material, which is called the eel- 

WTiat are the three great cavities of the body ? What are their 
walls ? What do they contain ? What is said of blood-vessels and 
nerves in the different structures of the body ? What is said of the 
packing of the parts of the body ? 



20 FIRST BOOK IN PHYSIOLOGY. 

hilar menibrane^ is not only around all the muscles 
and between their fibres, but it is around everything 
and in almost everything in the body. It is full of 
little cells or spaces; and hence comes its name. In 
some parts these cells are larger than in others. The 
fat of the body is in cells of this substance, mostly 
just under the skin. When the cells contain fat they 
are larger than they usually are. 

17. This cellular substance is very yielding, so that 
the motions of the body are not made less free by 
their being thus bound together by this packing ma- 
terial. When the muscles are performing some of 
their motions this substance is very much moved and 
stretched, but it always yields easily and is not torn. 

18. The cells of this substance are kept moist by 
a very little watery fluid. When this fluid is in 
greater quantity than it should be, the disease called 
dropsy is present ; and it is because the cells every- 
where open into each other, that the water in this 
disease is so apt to accumulate in the lowest parts of 
the lower limbs. 

19. Over all the parts of the body is the skin cover- 
ing them up from our view. It also defends them 
from injury. While for this purpose it is very firm, 
it is at the same time quite yielding, so that it may 
not restrain the motions of the body. Underneath 
the skin the cellular substance is very abundant, con- 
necting the skin with the muscles and other parts. 

20. There is a kind of skin, called the mucous 

Describe the appearance of the common packing material. What is 
eaid of the fat ? \\' hat is said of the yielding character of the celliilai 
membrane ? What is said of its cells ? What is said of the skin ? 



DIFFERENT STRUCTURES OF THE BODY. 21 



meiDbrane, that begins in the mouth and nose, and 
lines all the passages to the lungs, the stomach, and 
other organs. It may be called the interior skin of 
the body. It is termed the mucous membrane, be- 
cause it is moistened by mucus, a glairy fluid which 
constantly oozes from it. The red covering of the 
lips does not seem to be either skin or mucous mem 
brane, but a texture somewhat like both of them. 

21. The serous membranes are so called because 
they are moistened with a watery fluid called serum. 
They line the outside of some of the great organs of 
the body, and also the inside of the walls of the cavi- 
ties that hold them. Thus the lungs are covered with 
a serous membrane, and the inside of the walls of the 
chest is lined with it. You can see what the object 
of this is : as the chest moves in breathing, the lungs 
rub a little against the walls of the chest ; but the 
smooth shining serous membrane that lines them pre- 
vents the rubbing from doing any harm. The same 
thing is true of the organs in the abdomen. The rub- 
bing of the stomach and the intestines against each 
other and against the walls of the abdomen, would 
make them sore and inflamed, if they were not all 
lined with this smooth and moistened membrane. 

22. 1 have not described to you all the structures 
in the body, but only those that it is well for you to 
understand in the beginning. You will know more 
in relation to these as I proceed, and I shall also d(!- 
Bcribe to you in the succeeding chapters some othet 
structures. 

What is said of the mucous membrane ? What is said of tie red 
Bkiu of the lips ? What are the serous merrbraLes? What (^o they 
line? ^^t'what use are they in the chest, and \u the abdomen 



22 FIRST BOOK IN PHYSIOLOGY. 

CHAPTER III. 
DIGESTION. 

1. I HAVE already told you in the first chapter that 
the blood, which is the common building material of 
the body, is made out of the food that we eat. That 
this may be done, the food must be digested^ as it is 
termed. 

2. Digestion is not a single and simple process: 
several things are done. First, the food is cut and 
ground by a sort of mill in the mouth ; and while this 
is going on the food is thoroughly moistened by a 
liquid called the saliva. As fast as it is ground and 
moistened it is passed through a tube that extends 
from the back part of the throat down into the stom- 
ach. There the food is mixed with another liquid 
called the gastric juice. It is then passed on into the 
intestines. There all that part of the food that can 
be used to make blood is sucked up by a multitude of 
little vessels. These vessels join together to form a 
tube which empties itself into the blood. Having thus 
described in a general way the manner in which the 
nourishing part of our food is separated and extracted 
from it, let us look at the different parts of the pro- 
cess more particularly. 

3. First, the food is cut and ground up by the 
teeth. The teeth, in order to be fitted for this work, 

From what is the blood made ? Is digestion one simple process 
What is first done to the food ? By what is the food moistened f 
What is done with it after it is ground and moistened ? What is mixed 
with the food in the stomach ? Into what does it pass from the stom- 
ach ? What is done with it in the intestines ? 



DIGESTION. 



2S 



are made very hard. They are the hardest sub- 
Btances in the body. None of the bones are as hard 
as they are. Their hardness is owing to the enamel. 
This forms a thick coat over all the body of the tooth 
down to the gum. It does not extend down on the 
roots, for it is not wanted there. The roots and all 
the inner part of the teeth are like common bone. 
The roots are fitted into sockets in the jaws so firmly 
that, as every one knows, it is very hard to pull thein 
out. 

4. In Fig. 8 you see a representation of half of the 
teeth of the upper jaw. Notice the difi*erence in their 




jhape. Kt aa are the two front cutting teeth. They 
nave sharp edges. Kt ddd are the three large back 
teeth. These have, instead of cutting edges, broad 
irregular surfaces, so that they can grind the food be- 
tween them and the same teeth in the lower jaw. At 
cc are two smaller grinders. At h is what is com- 
monly called the eye-tootli. It is so shaped that it 
neither cuts nor grinds, but tears. The tootli in the 



What is said of the teeth? What is the enamel and how is it ar 
ranged on the teeth? Describe the different kinds of teeth in man? 



tM 



FIRST BOOK IN PHYSIOLOGY. 



Fig. 9. 



lower jaw that is like it is called the stomach-tooth. 

You see then that man has three kinds of teeth for 

eating his different kinds of food, viz., cutting, teai 

ing and grinding teeth. 

5. Different animals have 
different kinds of teeth, ac- 
cording to the kinds of food 
which they eat. In Fig. 9 
you see the teeth of an ani- 
mal that lives on flesh alone, 
called a carnivorous animal. 
The front teeth are tearing 
ones, while the back teeth 

have sharp edges for cutting. The flesh is first torn by 




the front teeth, and then it is cut up by the back ones. 
You can see these two kinds of teeth in the mouth of 
the dog. The tearing teeth are long. When the jaws 
are closed the ends of these teeth do not press upon the 
ends of the teeth that are opposite to them, but 
the teeth pass by each other, as you see in Fig. 10, 

Fig. 10. 




Describe the teeth of carnivoroui^ animals. What arrangement ol 
ibeir tearinsr teeth ^ives tliem orreat ]30wor? 



D I G E S T I IN . 



z;> 



Fig. }.1. 




which is a representation of the jaws of a tiger. You 
see at once that this arrangement of these long tear- 
ing teeth gives them great powder in tearing flesh t«» 
pieces. 

6. Animals that live on vegetable food, called /t^r 
bivorous animals, have no tearing teeth. The horso 
and the cow are of this class. They have tw^o kinds 
of teeth. There are cutting teeth in front, by which 
they crop the grass or draw the hay from the rack. 
There are also grinding teeth by which they grind up 
the food before they swallow it. In Fig. 11 you so^ 
the rough surface of some of 
these teeth. There is a pecu- 

iar arrangement of the enamel, 

which admirably fits them to 

grind up the fibres of the grass. 

merely on the outside as it is in our teeth, but tliere 

are ridges of it, as you see, standing up in the middle 

of each tooth. 

7. Those animals that live on soft 
fruits do not need such grinders as 
the grass-eating animals do. They 
therefore have rounded teeth which 
serve to crush their food as repre- 
sented in Fig. 12. 

8. In the cutting, and tearing, and grinding of our 
tood the lower jaw is moved against the upper one 
by means of muscles. They are the workmen of tlie 
mill, as we may say. These muscles w^ork diff'erently 



The enamel is not 



Fig. 12. 




Describe the teeth of herhivoroiis aoiaials. Wljat peculiar arrange 
iiieot of the enamel do they have ? What are the teeth of .animals thai 
eat soft fruits ? 
9 



*2t> FIRST BOOK JN PHYSIOLOGY. 

n different animals, according to the kind of food 
and according to the character of the teeth. Thus, 
when an animal eats vegetable food and has grinding 
teeth, the muscles have the power of making the 
grinding motion. If it were not so, the grinding teeth 
could not grind, but could only crush. You can see 
the difference between the grinding and tearing motion 
of the jaws, if vou watch a dog and a cow while they 
are eating. The dog, as he tears his food, moves his 
lower jaw up and down against the upper jaw like a 
hinge. But the cow, as she chews her cud, gives to 
her jaw a side wise motion, together with the hinge- 
like motion, and thus grinds the food. The dog does 
not need to grind his food as the cow does, and there- 
fore he has no grinding teeth and no muscles that can 
perform the grinding motion. 

9. Man eats all kinds of food, or is omnivorous ; 
he therefore has the various kinds of teeth. But ob- 
serve, that his grinding teeth are not such thorough 
grinders as the cow^ and the horse have. He does not 
Qced the ridges of enamel to grind the vegetable food 
that he eats, most of which he softens by cooking it. 
Observe, too, that his tearing teeth are not so long 
and so powerful as those that you see in the mouth 
of the dog and the tiger. The reason is, that he 
knows how to invent and use cutting instruments, and 
therefore divides his food very much before he eats 
it. 

10. As the food is cut and ground by the teeth, i 

Illustrate tbe differenee in the -working of the muscles in the carnivor 
ous and herbivorous. Why is man called omnivorous ? Why are \m 
grinding teeth less powerful than they are in animals? 



DIGESTION. ^'i 



is well moistened by the fluid in the mouth called the 
saliva. This fluid is made in some glands in the 
neighborhood. The laro:;est of these glands, or saliva- 
factories, as we may call them, is just under the ear. 
It is this o-land that is so much s^velled in the disease 
called mumps. There are three pairs of these glands, 
and they have ducts or pipes going from them, which 
open on the inside of the mouth. They are always at 
work making the saliva to keep the mouth moist, but 
they are especially busy while we are eating, in ordei 
that the food may be properly moistened. 

11. All these three pairs of factories do not make 
the same kind of fluid. One pair make a fluid which 
is a little thicker than that which is made by the other 
two pairs. It is curious to see the reason of this dif- 
ference. The thin fluid is mixed with the food while 
the mill is grinding it. The thick fluid is not poured 
out at all while this is going on ; but the moment 
that we stop chewing, and the food is thrust back into 
the throat to be swallowed, the thick fluid is poured 
out and covers the food, so that it may slip down 
easily into the stomach. 

12. The tube through w^hich the food passes down 
mto the stomach is called the oesophagus, or gullet. 
In Fig. 13 is represented the inside of the stomach with 
the beginning of the intestines. At 3 is the left end 
and at 4 is the right end. At 1 is the opening of the 
gullet into the stomach. At 5 is a valve which is 
sometimes shut, so as to prevent anything from pass- 
By what is the saliva made ? Where is the largest of these glands 

situated? How many of these glands are there? Are they equally at 
work all the time ? Do they all secrete the same kind of fluid ? Wha^ 
tM the use of the thicker fluid made by one pair of these glands? 



28 



FIRST BOOK IN PIIYSIOLOGX, 



Fie. 13. 




ing from the stomach into the intestine. This vaive 
is called i\i^ pylorus. 

13. Wliile the food is in the stomach the gastric 
juice oozes out from all the inside lining, marked 8, 
and mixes up with the food. The mixture is verj 
thoroughly made, because the stomach keeps up a 
sort of churning motion. After awhile the food, 
although it is sometimes of so many different kinds, 
is all changed into a greyish cream-like substance, 
called chyme, 

14. None of the food can pass by the valve into the 
intestines till the gastric juice has acted upon it 
enough and changed it into chyme. As the stomach 
churns the food, some of it continually comes in con- 
tact with the valve. But the valve will not open till 
some of it comes along that is fit to pass. If the food 



Describe tlie stomach as shown in Fig. 13. Where does the gastric 
juice come from ? How is it mixed thoroughly with the food ? What 
IS the chymeJ Describe the operation of the v>^lve called the pyloms. 



DIGESTION. 



29 



is not digested, as sometimes happens, then commonly 
this sentinel after awhile gives up its resistance, and 
lets the undigested food pass on. Or, if it holdii out 
in its resistance, the food is got rid of by being throwii 
l)ack by the stomach through the oesophagus or gullet. 
15. When the chyme passes through the valve of 
the stomach it goes into the intestine, the beginning 
of which you see in Fig. 13. There two otlier juiccF 

Fig. 14. 
Liver. Pylorus. CEsophagus. Pancreas. Stomach. 




'pleen 



Large Intestines 



/ — Small Intes'ines 



Small Intestines. 

are poured in and mingled with it. The duct froui 
the liver is represented in the figure at 6, and the due 

IdIo what does the cbjme pass from the stoinaeli ? What two juice. 
are lure mingled with it? 



30 



FIRST BOOK IN PHYSIOLOGY. 



from the pancreas opens near it. These fluids come 
from two glands. One of these glands is a very large 
one, the liver. You see this gland in Fig. 14, which 
gives a general view of the digestive organs. The 
juice from this gland is called bile. It is of a yellow 
color and is very bitter. The other juice comes from 
a gland called the pancreas, which you see in the 
figure, lying behind the end of the stomach. This is 
very mild and is mucli like the saliva wath wdiich the 
food is moistened while the teeth are grinding it. 

16. There is a curious arrangement of the bile duct 
or duct from the liver, which I will notice. While it 
goes direct from the liver to the intestine, like the 
duct from the pancreas, a branch goes back from it 
to the gall-bladder, as it is called. This arrangement 
IS represented in Fig. 15, in which a is the intestine, 
cut open, 1) is the duct which is made 
by the joining together of many little 
ducts from the liver, c is the gall-blad- 
der, and d is the duct w^hich goes from 
the gall-bladder to join the duct from 
the liver. The object of this arrange- 
ment is plain. The bile is needed in 
the intestine in considerable quantity 
w^henever there is chyme there for the 
bile to act upon. But the liver is a 
large organ, or a large factory, as w^e 
may call it, and is all the time making 
l)ile. The gall-bladder is a convenient place of de- 
posit, or reserv^oir, where the bile is stored up until it 




^roiu what glands do these juices come ? Describe tlie arrangement 
tlie gall-bladder an-^ th^ iuets. 



D I (t E S Tl O N . 



is needed. When there is no chyme in the intestine, 
the bile, as it flows from the liver in the duct 5, takes 
a turn by the branch d into the gall-bladder. In what 
way it is made to take this sharp turn we do not 
know. After we have eaten a meal, and the chyme 
beginG to be poured from the stomach into the intes- 
tine, then much bile is needed, and it comes freely 
both from the liver and from the gall-bladder. 

17. We do not know exactly what the bile and the 
juice from the pancreas do to the chyme. It is sup- 
posed that they separate the nourishing part of the 
chyme from that which is not nourishing, as the chyme 
passes along through the intestines. As this chyle (sc- 
called) is thus separated, it is sucked up or absorbed 
by vessels scattered all over the inside of the intes- 
tines. These absorbents are called lacteals, from lac. 
meaning milk, because the fluid which they absorb 
is a milk-like fluid. 

18. The lacteals are exceedingly small, and cannot 
be counted. They do their work very faithfully. 
They will commonly take up nothing but the chyle. 
Anything else that comes along they shut their mouths 
against and let it pass on. 

19. The chyle is that which makes all the blood. It 
must therefore in some way be poured into the circu- 
lation, and I will tell you how this is done. The lit 
tie vessels that drink it up from the chyme unite to- 
gether to form a tube about the size of a quill. This 
tube runs up in front of the back-bone, and at the to]> 

What is the office of the gall-bladder ? What effect do the bile an** 
juice from the pancreas produce upon the chyme ? What is the chyl<> 
What are the lacteals? 



<i2 FIRST BOOK IN PHV.SIOLOGY 



of the chest em23ties the chyle into the blood where 
two large veins unite together. And now this whitish 
milky fluid becomes blood, and is carried every- 
where to nourish the body. 

20. In Fig. 14 you see all the complicated apparatus 
or machinery of digestion, except its mill or grinding 
part where 'the process begins. The parts are not 
closely packed together as they are in the body, but 
they a3'o represented as a little separated from each 
oth^r, so that you may see them more clearly and 
fully. As this is a front view the left side of the 
figure is the right side of the parts. " The large end of 
the stomach, which is at the right side of the figure, 
is on the left side in the body. You see that the 
great bulk of the liver is therefore on the right side. 
The spleen, which lies against the large end of the 
stomach, is an organ the use of which we do not 
Linderstand. Neither does any one know Avhat is the 
use of the little worm-like appendage at the beginning 
of the large intestines. 

21. The great object of all this apparatus is to ex- 
tract the chyle, the nutritious part of the food, and 
pour it into the blood. It is in this way, iv^at blood ie 
made out of our food. The blood, the building mate- 
rial of the body, is all the time used in building and 
repairing. For -his reason there must be a constant 
fresh si:pply of bV)od. It is the chyle poured into 
the blood by its litrle tube or duct that gives this sup- 
ply. If this tube should be cut ofl"', or be blocked up. 



Describe the way in which the chyle gets into the blood. What do 
it become? Describe the arraog-emeiU of the organs of digestion 
Fio-. 14. Wiiat is the object of all the apparatus of digfestion '« 



DIGESTION. 33 



the blood would constantly lessen, the body would 
shrink or become emaciated, as w^e say, and death 
would at length result. The same thing would hap- 
pen if the stomach stopped digesting the food, for 
then no chyle would be formed, and therefore no new 
blood would be made. 

22. There are many things that are yery wonderful 
in all this process of blood-making, which is executed 
by this complicated machinery of digestion. It is 
especially wonderful that a simple milky fluid should 
be separated from such a great variety of food as we 
eat from day to day, and then that this whitish fluid 
should be cliano;ed into red blood. 

23. The apparatus of digestion differs in different 
animals according to the kinds of food that they eat 
If the food that an animal eats is very much like his 
body, the apparatus or machinery is quite simple ; for 
the food in this case does not need to be changed 
much to make his blood. But if the food wdiich an 
animal lives on is very much unlike his flesh, the 
apparatus of digestion is very complicated, because 
the food must be much changed before blood can be 
made out of it. 

24. For these reasons the digestive machinery in 
such animals as the dog, the tiger, and the lion, is 
simple, for they live on flesh, which is of course very 
much like their own flesh. But in such animals as 
the cow and the sheep, this machinery is complicated. 

In what ways can the supply of chyle to the blood be stoppecU 
What thmgs are there in the process of digestion that are especially 
wonderful ? In what animals is the machinery of digestion most simple'^! 
In what ani uals is it complicated ? Illustrate by referring to different 
animals. 

2* 



M 



FIRST BOOK IN PHYSlOLOCiY. 



The reason is, that the grass which they eat is not at 
all like their flesh. It must therefore go through a 
M-reat chano^e to fit it to make the blood and flesh of 
such animals. And this cannot be done without con- 
siderable machinery. The flesh-eating lion has a 
single stomach, and the length of its intestines is only 
three times that of its body. But the grass-eating 
sheep has really four stomachs, and the length of its 
intestines is twenty-eight times that of its body. Fig. 
16 represents the four stomachs of the sheep. In man 

Fig. 16. 



CEsophagus- 




3d Stomach 



Intestine- 



Pylorus.- ^^^ g^^^^ 2d stom. 1st Stom. 

there is but one stomach, and the length of his mtes- 
tines is about six times the length of the body. 

25. In birds that eat grains and seeds there is a pe- 
culiar arrangement of the digestive machinery. They 
have no teeth, and their mill for grinding their food, 
instead of being in the mouth, is in the stomach. The 
gizzard, which is the stomach, is truly a mill for 
crushing the food to pieces. It has on the inside two 



How long are the intestines in t]:e lion? 
How many stomachs has the sheep? 



In the sheep ? In man! 



DIG E^TION. 



3D 



very hard surfaces, whicli are rubbed and pressed 
together by stout muscles. The grain is thus broken 
np just as it is done between two mill stones. While 
this is going on the gastric juice comes down fron: 
bove, and dissolves and digests the broken grain 

Fig. 17. 




Thit airangement is seen in Fig. IT, which represent.! 



\V ,at. is there peculiaj- in the digestive machinery of grain-eatiDj 



3G FIRST BOOK IN PHYSIOLOGY. 

the stomach of a turkey. At h is the gizzard cut 
open^ showing the two hard grinding surfaces, and at 
a above is the part from which oozes the gastric juice. 
In those birds that live on flesh or fish there is no such 
grinding machinery, but the stomach is a thin bag< 
just as it is in all animals that live on such food. 



CHAPTER IV. 

CIRCULATION OF THE BLOOD. 

1. In the last chapter you saw how the supply ot 
blood is kept up in the body. In this chapter I shall 
show you how the blood is circulated everywhere, in 
order that it may be used in building and repairing. 
The machinery that thus circulates the blood is called 
the cirGulating system. It has its pipes everywhere. 
There is no part of the body where the blood does noi 
go. And this machinery keeps the blood everywhere 
in motion. It nowhere rests for a single moment. 

2. This circulating machinery has a great central 
organ, the hearty situated in the chest. This forces 
the blood out all over the body through the arteries. 
It receives it back again by the veins. It forces the 
blood out through a large artery, called the aorta, and 
from this go branches in every direction. These 

Describe the aiTangeraent of the digestive organs in the turkey. 
What kiud of stomach bave birds that eat flesh or fish? What is the 
niachiuery that circuhates the blood called ? Is the bL'od ever still any 
where ? W^hat are the different parts of the macliinery ? Through 
what does the heart send out the blood ? Through what does it receive 
it back I 



CIRCULATION OF THE BLOOD. 37 

branches divide more and more, jnst like the branches 
of a tree, till the extreme branches are exceedingly 
small. 

3. These sn)all arteries end in a network of vessels 
that are so small that they are called cajjillaries^ from 
the Latin word cajpilla^ hair. They are really smaller 
than any hair. AVhen you prick or cut your finger 
you wound a large number of these capillaries, and 
they let out their blood. 

4. The heart acts like a forcing and suction pump 
It pumps out the blood through the arteries,, and by 
suction it drawls the blood back by the veins. It 
forces out the blood by contracting itself, or making 
itself smaller. It draws in the blood by dilaiing 
itself, or making itself larger. 

5. I will make these tw^o actions of the heart plain 
to you by certain comparisons. When you press the 
two sides of a pair of bellows together by the handles^ 
as represented in Fig. 18, you contract the bello*vs — 

Fig 18. 



that is, you make the room in it smaller. A part o« 

What are the capillaries? Like what does the heart avt? Ho^v 
does it force out the blood ? And how does it (h*aw it in? Illu6irati» 
bv comparison \\\\h a pair cf bellows 



38 



FIRST BOOK IN PHYSIOLOGY. 



the air is therefore forced out through the nose of the 
bellows. It is in the same way that the blood is 
forced out of the heart through the aorta. The only 
difference is that the heart contracts itself, instead of 
having it done, as in the case of the bellows, by hands 
and handles. Again, when you move the handles of 
the bellows apart, as represented in Fig. 19, yon 

Fio. 19. 




enlarge the room in the bellows, and so the air rushes 
in to fill the vacant space. In like manner, when the 
heart dilates, or enlarges itself, there is more room in 
it, and the blood rushes in to fill it up. 

6. Another comparison, to illustrate the contraction 
and dilatation of the heart, is this. Fasten a tube to 
the neck of an India- rubber bottle, and fill it up 
with water. Put the end of the tube in a vessel of 



Illustrate tb( 
rubber bottle. 



action of the heart by the comparison of the india 



UlRCULATlON OF THE BLOOD. 



3^ 



water. If now you press the sides of the ball together 
some of the water in it is forced out into the vessel, 
just as blood is forced out through the aorta, when 
the heart contracts. If now you stop pressing the 
ball, and let it take its round shape again, the water 
rushes into it from the vessel. For the same reason, 
when the heart dilates or becomes larger, the blood 
rushes into it. 

7. I will now explain to you the manner in which 
the heart contracts and dilates. The heart is made 
up of muscular fibres, which have the power of short- 
ening themselves, as you saw in chapter second, §7 and 
§ 8. Now suppose one of these fibres, as seen at «, in 
Fis^. 20, shortens itself so as to be like 5, the space that 

Fig. 20. 





IS inclosed in it becomes smaller, just as in the case 
of the bellows. In g and d you see the same thing 
represented when several fibres are together. If the 
fibres in c become shorter, so as to be as in c?, the 
space they inclose is smaller. You readily see from 
this, that when all the fibres of the heart are short- 
ened, the space in it is lessened, and a part of the 
blood is forced out. 

8. You can see by the same figures how the lieart 



Explain by the Figures the action of the muscular fibres of the hcarl 
when il contracts and dilates. 



40 FIRST BOOK IN PHYSIOliOGY. 

dilates or enlarges itself. If the contracted or short- 
ened fibre h lengthens so as to be as a^ the space en- 
closed by it becomes larger. And so also of any 
number of fibres. It is supposed that the enlarged or 
dilated state of the heart is its natural state of rest^ 
when the fibres are not acting, but are quiet. That 
is, the heart is really at work only when it contracts. 
When it dilates it merely ceases to act, and lets itself 
go back to its natural size by its own elasticity, as it 
is termed. It is just as the india-rubber ball goeai 
back to its natural roundness when you stop press- 
ing it. 

9. The fibres of the heart are not arranged in the 
regular form in w^hich they are represented in the 
above figures. They meet each other, and cross each 
.>ther in various ways. But the eff'ect of their contrac- 

FiG.21 . ^ tion is as described. You can see, 
for example, by figure 21, that it 
wall make no diff*erence in the 
eff'ect, whether a single fibre go 
all around, as in a^ or w^hether 
two fibres lap on to each other, as 

in 5, and are fastened together. And the same can 

be said of any number of fibres. 

10. When the heart beats, these fibres shorten 
themselves, and the blood is forced out into the arte 
ries. Then, as the fibres relax, the blood comes into 
the heart from the veins. And so the heart by turiia 
contractsand enlarges, just as you contract and enlarge 
tilt; bellows in working them, as you blow the fire. 

Is the heart m actioa, or is it at rest, when il dilates ? How are th# 
•fibres of the heart arranged? G-ive the comparison made in §10 be 
tweeii the arrtion )f thp.se fibres and the action of the beUows. 




CIRCULATION OF THE BLOOD. 41 

11. Let us look now at some things in which the 
arteries and veins differ from each other. You see 
veins lying just under tlie skin in various parts of the 
body, but you do not see the arteries They all lie 
deeper than these veins that you see. The reason is 
this. It would be dangerous to have the arteries so 
near the skin as some of the veins are. For the heart 
is punaping the blood directly into them with great 
force. And therefore if an artery is cut, it bleeds 
much more than a vein of the same size, and its bleed- 
ing is not as easily stopped. For this reason the 
Maker of our bodies has, as we may say, laid the 
arteries deep, so that they cannot often be cnt in the 
accidents that happen to us. 

12. You can see that special pains are taken in 
some cases to guard the arteries. Thus the large 
artery of the arm, when it comes to the joint at the 
elbow, does not pass over the bones, where it would 
be apt to get wounded. It lies deep on the inside of 
the elbow, under the stout tendon that you feel there. 
So at the knee, the artery is deep in the ham at the 
back of the joint, in a space between two jutting par- 
apets of bone, as we may call them. 

13. There are only a few places in the body where 
arteries of any size are very near the surface. In such 
cases it is because they could not possibly be laid in 
any better way. One of these is the wrist, where the 
physician commonly feels the pulse. Another is on 
the temples. In some persons who are .very thin you 

How do the arteries aud the veius differ from each other in theii 
situation? What is the reason of this difference? Mention 8oni« 
nases in w'\ich special pains are taken to guard the artei'<^s 



42 FIRST BOOK IN PHYSIOLOGY. 



'^SLii see the artery on the temples beating, and can 
count the pulse there without being obliged to feel it. 

14. As the heart pumps the blood into the arteries 
with so much force, they are made much stronger than 
the veins are. If they were not, they would often 
burst, as you have seen the hose of a fire engine do. 
But the arteries are made so strong that this is a very 
uncommon accident. 

15. What is called the pulse I will explain to you. 
' When the heart contracts it gives a sudden motion or 

impulse to all the blood in all the firm arteries. The 
blood all moves at once. The motion is not like a 
wave, going from the heart in all directions. The 
blood at a distance from the heart is moved at the 
same time with the blood near the heart. It is this 
motion or impulse that you feel when you put your 
finger upon an artery. The impulse thus felt is called 
the pulse. You can feel the pulse wherever you can 
feel an artery. It is everywhere. In a young infant 
you can both feel and see the pulse in the open space 
on top of its head, where the bones are not joined 
together. This is the pulse of the arteries of the 
brain. When the heart beats very strongly, as it 
does in a high fever, this pulse in the brain is very 
manifest. 

16. If a vein be cut, the stream from it is a steady 
:>ne, because the blood flows in the veins back to the 
heart slowly and steadily. But if an artery be cut, 
the stream is not steady but spouts out by jerks or 

In wh'-ifc places in the body are the arteries very near the surface, 
and why ? How do the arteries and veins differ in strength, and why f 
Explain what the pulse is. Where can you feel the pulse? 



CIRCULATION OF THE BLOOD. 43 



jets. This is owing to the impulse that is given to 
the blood in the arteries when the heart beats or con- 
ti*acts. There is a jet for every contraction. 

17. It is well for every one to know^ how to stop 
A\e bleeding of an artery when it is wounded. It does 
nc good to wind cloths around, as is very commonly 
done. This only catches the blood, while the artery 
is left to go on to bleed. If you bear in mind that 
the blood comes from the heart in the artery, you will 
see that pressing on the artery on the side of the 
wound w^hich is towards the heart will stop the bleed- 
ing. Firm pressure with the thumb will do it if you 
put the thumb in the right place. In order to find 
the right place uncover the wound and press your 
thumb here and there till you see that the blood stops 
flowing from the wound. If you find that by pressing 
in any spot the blood is stopped, hold your thumb 
there till the surgeon comes to take care of the case. 
If you cannot find the right spot, tie a slip of cloth or 
a handkerchief around the limb above the wound, 
and then twist a stick in it till the bleeding stops. A 
child with this inform.ation may be able to save a life, 
and yet for want of it many a person has died in such 
a case, for few even among adults understand the 
matter. 

18. The object of the machinery of the circulation 
is to get the blood into the netw^ork of the capillaries, 
and then bring it back to the heart. It is when the 
blood is in these capillaries that it is used for building 

How does the stream of blood from a cut vein differ from the stream 
from a cut ai'tery ? What is the reason of the differeuee ? How would 
vov ttop tli<> bleeding of ao artery ? 



34 FIKST BOOK IN PHYSICLOGf. 



and repairing. It is by the arteries, as jou have seen^ 
that the blood is brought to the capillaries, and it is 
by the veins that ii is carried back from them to the 
heart. 

19. As the blood comes from the heart by the arte- 
ries it has a bright red color. But when it passes 
from the capillaries into the veins it has a dark color 
The cause of this change is the use which is made of 
the blood while it is in the capillaries. Something 
has been taken from it for building and repairing, and 
so it cannot be as good building material as it was 
before it was used. Not only has there something 
been taken from it, but there has also been added to 
it some of the waste matter that conaes from the weai 
and tear of the system. On becoming dark blood, 
then, it has been changed from good blood to bad blood 

20. This dark blood, then, that goes back by the 
veins to the heart is not fit to be used so long as it 

, remains dark. When it gets back to the heart it will 
not do to have it sent all over the body by the arte- 
ries. It would destroy life everywhere. The organs 
of all the machinery of the body would stop their 
operations. For example, if this dark blood should 
be sent to the brain, the individual would become ir 
sensible and fall down, and he would die very soon it 
the good red blood could not be sent to his brain. 
And so, too, would all the organs stop work, as we may 
say, if dark blood instead of red were sent to them. 

What is done with tlie blood in the capiUaries ? What is the color 
of the blood in the arteries ? What in the veins ? What is the cause 
of the change ? What is done to the blood in the capillaiies f What' 
■;70uld happen if the dark blood should be sent to the organs of tha 
body instead of red blood ? 



CIRCULATION OF THE BLOOD. 



4.^ 



2.1. This dark blood then, when it comes back tc 
the heart, nuist in some way be changed to red blood 
before the heart sends it again all over the system. 
For this purpose the heart sends it to the lungs, w^here, 
by exposure to the air that we breathe into those 
organs, it is changed to red blood. After it is thus 
changed it comes back to the heart, and is then sent 
all over the body. 

22. All this could not be done by the heart if it 
were a single organ. . It is not single. It is double, or 
rather, there are really two hearts; one for the circu- 
lation all over the body, and the other for the circu- 
lation through the lungs. The two hearts are so 
closely united together that they are spoken of as one 
heart. But they are entirely separate, so far as any 
communication betw^een them is concerned. None 
of the blood in one can mingle with that in the other. 
The blood in them is different. In one heart it is 
red, and in the other it is dark. I shall speak of them 
as the two sides of the heart, the right and the 
left side, as is common- 
ly done. 

23. That you may 
understand the course 
of the blood in the two 
circulations, I shall de- 
scribe it by Figure 22. 
Let a represent the 
right side of the heart, 
c. the left side, h the 



Fig 22. 




What is floue with the dark blood ? Why is the heart double ? Are 
l.iie two sides of the heart as separate as if they were two hearts ? Is 
\iie blood of the same eolor in the two sides ? 



46 FIRST BOOK IN PHYSIOLOGY 

lungs, and d the general system of the body. 
The arrows point in the direction in which the blood 
flows. In all the shaded part the blood is dark, and 
in the part that is not shaded it is red. Let ns now 
begin at some point, and trace the course of the 
blood. We will start at a^ the right side of the heart. 
The blood received here from the whole body by the 
veins is of a dark color. It is sent by this right side 
of the heart to the lungs, 5. Here it is changed to 
red blood, and then passes back by veins to the heart 
— but observe, it is to the left side, g. It is now sent 
by this left side of the heart to the whole system, d. 
Here, in the capillaries, it is changed to dark blood, 
and goes back by veins to the right side of the heart, 
% where we started. The blood is constantly going 
the rounds of these two circulations, day and night, as 
long as life lasts. 

24. The blood in the right ^ide of the hearty or the 
heart for the lungs, is dark. The blood in the left 
side of the heart, or the heart for the whole body, is 
red. So also in the arteries that go out from the right 
side of the heart the blood is dark, while that which, 
goes out in the arteries from the left side is red. And 
while dark blood is brought in the veins to the right 
side of the heart from the whole body, the veins that 
come to the left side from the lungs contain red blood. 
That is, in the circulation for the lungs the dark 
blood is in arteries and the red in veins, but in the 
circulation over the whole system it is just the 

Describe the course of the drculation as represented in Fig. 22. In 
\rhich side of the heart is the blood red, and in which dark ? How is it 
in tlie arteries and veins of the two cireuhitions \ 



CIRCULATION OF THE BLOOD. 



47 



reverse — the dark blood is in veins and the red is in 
arteries. 

25. Tlie heart is not only two separate hearts, bn* 
each of these has two apartments in it. One of these 
apartments is larger than the other. The smaller 
apartment is called the auricle and the larger the 
ventricle. This arrangement is represented in Fi^. 23. 

Fig. 23. 




The middle part of the figure represents the heart 
with its two sides, that have no communication with 
each other ; a being the right auricle, h the right ven- 
tricle, d the left auricle, and e the left ventricle. The 
blood is received in the right auricle, a^ from the 
general system, y. It then passes into the right ven- 
tricle, J, and is forced by the contraction of it through 
arteries to the lungs, c. From the lungs it comes back 
to the heart, to the left side, and enters the left auri- 
cle, d. From this it passes into the left ventricle, e^ 
from which it is sent all over the body, repre- 
sented by/*. 

Describe the apartments of th^ heart. Describe the circulatioD as* it 
takes phice throuu^b tliese apartments* 



48 FIRST BOOK IN PHYSIOLOGY. 

26. In each half or side of the heart the ventricle 
is the main apartment. It is much larger than the 
auricle. The auricle is a sort of entrance-chamber 
to the main apartment, the ventricle. There are 
valves, or folding doors, as we may call them, between 
these two apartments. These valves are so arranged, 
that the blood can pass only one way. Take, for 
example, the valves between the right am^icle, a, and 
the right ventricle, h. The blood can go from a to &, 
bu't it cannot go from 5 to a, 

27. I will describe to yon the manner in which the 
blood is made to go through these two apartments. 
When the auricle a dilates or enlarges, it draws in 
the blood from the veins of the body. It then con- 
tracts and forces the blood into the ventricle 5. The 
ventricle now contracts, and sends the blood towards 
the lungs, g. Now, when the ventricle h contracts, it 
would force the blood hack into the auricle a^ as well 
as forward towards the lungs, were it not for the 
calves. When the ventricle contracts these valves 
shut, and so none of the blood can go in that direc- 
tion, but all of it goes towards the lungs. 

28. These valves operate just as the valve of the bel- 
lows does, as seen in Figures 18 and 19, pp. 37 and 38. 
In Fig. 19 the hands are drawing the handles apart, 
and enlarging the space in the bellows. Here the 
valve is open and the air is rushing in, just as the 
valves of the ventricle open and the blood rushes in 
when the ventriele dilates or enlarges. In Fig. 18 

How are the valves between these apartments arranged ? Describe 
the action of the auricles and ventricles. Compare the operation of the 
valves between them to that of the valve of the bellows as represented 
In Figs. 18 and 19. 



CIRCULATION OF THE BLOOD. 49 



the hands are pressing the liandles together, and the 
valve is shut, and the air is forced out through the 
nose ; just as, when the ventricle contracts, the valves 
close, and the blood is forced out through the artery 
that goes from the ventricle. Observe now, in what 
way the valves are shut in both cases, In the case 
of the ivellowsa when the handles are pressed together, 
the air escapes wherever it can. If the bellows are 
tight, il escapes only through the nose. If the valve 
does not fit well somie of it escapes there. The air, 
pressi/ig in all directions, shuts down the valve, and if 
the v?^lve is tight no air can get out there. Now, the 
blood does in the ventricle of the heart just as the air 
does in the bellows. When the ventricle contracts, 
the blood, in escaping from the pressure, shuts the 
val*?s. If the valves fit well, as they commonly do, 
none of the blood can go back into the auricle, but it 
will all go out through the artery, just as all the air 
goes out through the nose of the bellows, when the 
bellows are tight. There are other valves in the 
heart, which, with those that I have spoken of, are 
fully described in my larger work on Physiology. 

29. Having thus described to you the manner in 
which the blood circulates, I now show you in Fig. 24 
a representation of the heart as it really appears. It 
is a front view. At a is the right auricle. This re- 
ceives the blood from all parts of the body by two 
large veins h and ^, A bringing the blood from above, 
and i from below. At 1) is the right ventricle, which 
receives the blood from the auricle, and sends it to 

What shuts the valve in the bellows ? What shuts the valves in th« 
\ieart 5 



50 



FIRST BOOK IN PHYSIOLOGY. 



- Fig 24. 




the lungs by the pulmonary artery yi At c is the lett 
auricle, which receives the blood from the lungs by 
the pulmonary veins g^ g^ g. At d is the left ventri- 
cle. This receives the blood from the auricle, and 
forces it out all over the body through the aorta e. 
The aorta, as yoii see, sends off branches upward to 
the head and arms, and then bends downward behind 
the heart to send off branches to all the other parts of 
the body. 

30. You observe much irregularity in the arrange- 
ment of the tw^o sides of the heart, as they are called 

Dp.seribe the heart as it really appears, by Fiji' ^i. 



CIRCULATION OF THE BLOOD. 5l 

The auricle a and the ventricle I make the right side. 
The auricle c and the ventricle d make the left side. 
In this front view of the heart you see only a part of 
the left side. Much of the left auricle and the left 
ventricle are hidden behind the right ventricle. The 
aorta, e^ the large artery through which the blood is 
pumped out by the left ventricle, is at first also behind 
the right ventricle. 

31. The heart, with its four apartments and its four 
sets of valves, is a very complicated machine. Tet 
commonly it works well and easily. One part does 
not interfere with another. All the parts do not work 
at the same time, and there is a time for each part t" 
act. In this way the whole machine works harmoni 
ously. 

32. The two auricles act together, and the two ven 
tricles act together also. For example, the two ven- 
tricles contract together, the right ventricle pumping 
the dark blood into the great artery of the lungs at 
the same time that the left ventricle pumps the red 
blood into the aorta, the large artery of the body. 

33. The heart, as it works its four parts, the auri- 
cles and the ventricles, makes two sounds. These you 
can hear if you put your ear to any one's chest on the 
left side at its lower part in. front. You hear them 
better here than at any other spot, because the heart 
here come? so near to the walls of the chest. You 
hear a heavy and full sound, followed by a quicker 

What is said of the irregularity in the arrangement of the parts oj 
the heart ? What is said of tlie complicated character of the hearty 
and of its harmony in action ? What parts act toge. /.it ? Where can 
you best hear the sounds of the heart ? Why ? )escribe its twc 
pounds. 



;r2 



FIRST BOOK 1^ rHYSIOLOGY. 



and lighter one. The syllables lub-tiip are a good 
representation of these sounds. 

34. The heart is almost wholly covered up by the 
lungs. It is encased in a sack or bag, and around this 
there is considerable of the common packing material 
of the body, the cellular membrane, spoken of in the 
second chapter. In Fig. 25 you see the heart betweei» 




f g h i 

the two lungs. The lungs are represented as drawn 
apart, so that you may have a full view of the heart 
with its arteries and veins. The sac of the heart and 
the packing material are also removed. At a is the 
trachea or windpipe ; on each side are the two arteries 
that go to the head ; c is the artery that goes to the arm 
h h are the veinr, coming from the head, and d d the 



With what is tb aeart covered ? Describe its situation as represent 
ed in Fig. 25. 



CIRCULATION OF THE BLOOD. 5.^ 

veins from the arms, all emptying, as you see, into a 
large vein that goes to tlie right auricle of the heart, e ; 
f is the large vein that brings the blood from below 
to this auricle ; g is the right ventricle, i the left, and 
It is the aorta as it goes down from the heart. 

35. The heart is commonly about the size of the 
closed hand of the individual. It is a very powerful 
organ for so small a one. It is composed of mus- 
cular fibres, and these are so nicely arranged that 
each fibre contracts exactly as it should to do its part 
of the work. 

36. The amount of work that the heart does in a 
lifetime is very great. In an adult it beats about 
seventy times in a minute. This is over one hundred 
thousand times in twenty -four hours. In the child it 
beats much faster than this. And it is to be remem 
bered that every time the heart beats each of its four 
parts contracts and dilates. Each beat of this organ 
is therefore a complicated movement of a very com- 
plicated machine. And this machine is alway^s at 
work as long as life lasts, alike while we are awake 
and while we are asleep, keeping the blood in motion 
in all parts of the body. 

What is the size of the heart ? Of what is it composed ? Abo'ji 
h(»w many times does the heart beat in a minute ? How many times 
in twenty foui hours ? How is it in children ? What is done in tli€ 
heart Id eTCvy beat ? Does the heart ever rest from its work * 



54 FIRST BOOK IN rHYSlOLOGT. 



CHAPTER V. 
RESPIRATION 

1. Yor saw in the last chapter that the dark blood 
IS sent to the lungs by the heart in order to be changed 
mto red blood. The great object of the machinery 
of the respiration is to bring the air and the blood to- 
gether, so that the air may produce this change. The 
way in which this machinery operates in doing this 1 
will explain to you in this chapter. 

2. The lungs fill up a large part of the chest. They 
are on each side of the heart, as you have seen in Fig. 
25. They are in common language termed the lights; 
and you can see what they are in man by looking at 
the lights of other animals. They are spongy bodies. 
They are full of very small air-cells. These give to 
them their spongy lightness ; and as a sponge is much 
larger when its cells are filled w^ith water than when 
it is dry, so the lungs swell out when tlieir cells are 
filled with air. This can.be shown to you with thv^ 
Lungs of some animal, as a sheep or a calf. If a tube 
be fastened to the windpipe, you can make the lungs 
swell out very much by blowing air into them. 

3. It is in these air-cells that the air changes the 
dark blood to red. But this is not done by mixing 
up the blood with the air in these cells. The blood 
is never mixed with the air except when in disease 

What is the object of respii-ation ? What is tlie situation of the 
lungs ? What is the cause of their lightness ? Mention the comparison 
between the ^ungs and a sponge. Is the blood mixed with the air in the 
'ungs ^ 



RESPIRATION 55 

blooi is raised from the lungs. In such a case the 
blood gets into the air-cells and air-tubes. But in 
health this never happens. The thin membrane or 
skin, that makes each air-cell, does not let the blood 
come through it. The air acts upon the blood through 
the pores of the skin, and of the capillaries that branch 
out upon this skin. It is by the airing that the blood 
thus takes, that every drop of dark blood that goes to 
the lungs is changed to red blood. 

4. The great object of the machinery of respiration 
is to keep the air going into and out of these air-cells. 
In this way fresh air is continually brought to the 
blood. When you breathe in, the air is forced into 
all these cells ; and when you breathe out, it is forced 
out of them. It is not all forced out. The lungs are 
never wholly empty of air. Enough is forced out to 
keep the air in the lungs constantly changing. 

5. Fig. 26 will give you some idea of the structure 
of the lungs. At d is the left lung, and at c are re 
presented the main branches of the windpipe that go 
to the right Inng, separated from the lung itself. At 
the lower part, at 6, are represented the very minute 
branches as they go to the air-cells. At h is the wind- 
pipe, and at a is the larynx, or Adam's-apple, as it is 
commonly called. It is through a chink in this that 
the air passes in and out as we breathe. 

6. I will now show by what machinery the air is 
forced into the lungs and out of them, and how it 
operates. You see that as you breathe the chest 



How does the air act upon the blood in changing it ? What does the 
machinery of respiration do ? Are the lungs ever wholly without air' 
D'^scribe tlie structure of the lungs by Fig. 26. 



56 FIRST BOOK IN PHYSIOLOGY. 




moves. No air would ever enter the lungs if thia 
nQovement of the chest vt^ere not made. If a bank ot 
earth should fall upon a man, and cover his whole 
body but leave his head free, the pressure of the earth 
upon his chest would prevent its moving. And so he 
would die for want of air in his lungs, unless the pres- 
sure were removed. 

7. When we breathe m, or make an inspiration^ as 
it is called, the air rushes into the lungs, for the same 
reason that the air rushes into the bellows when the 
handles are moved apart. In inspiration the space in 
the chest is enlarged, just as the space in the bellows 
is enlarged when the handles are moved apart. And 
because the space is enlarged air rushes in wherever 

What is said of the motion of the chest in breathing ? What is %v 
^piralion ? Why does air rush into the lungs in inspiration ? 



RESPIRATION. 



57 



it can get m 



In the bellows it comes in throngli 
both tlie nose and the hole in the side. In the chest 
it comes in only through the trachea or windpipe. 

8. In expiration^ that is, when we breatlie out^ the 
air is forced out through the trachea, for the same 
reason that the air is forced out through the nose of 
the bellows when you press the side^. together with 
the handles. In forcing the air uut of tho lungs the 
muscles about the chest do for the chest what your 
hands do for the bellows. 

9. If the bellows had no hole in the side, and the 
space in them were filled with a soft spongy sub- 
stance, so that the air coming in through the nose 
would go into all the spaces in this substance, the 
bellows would then resemble very much the chest 
with the lungs. In Figs. 27 and 28 is represented a 



Fig. 27. 



Fig. 28. 





pair of bellows thus arranged. In Fig. 27 the sides 
of the bellows are brought near together, and so some 
of the air is forced out, and the spaces or air-cells are 
small. ISo when expiration is performed by the chest 



Give the illustratiou of tlic 
3* 



bellows. What is expiration^ 



Db FIRST BOOK IN PHYSIOLOGY. 

the air-cells shrink as the air passes out of the trachea 
In Fig. 28 the sides of the bellows are moved apart 
and the air-cells are enlarged, the air rushing in 
through the nose to fill them up. Just so, when the 
chest expands in inspiration, the air-cells in the lungs 
enlarge, and the air fills them by rushing in through 
the trachea. 

10. That 3^ou maj understand how the movements 
of the chest are made in inspiration and expiration, I 

Fig. 29. 




must describe to you the structure of the chest. Its 
walls are made up of bones connected together chiefly 
by muscles. The bones that form the framework of 
Hie chest you see in Fig. 29. The spinal column h b 
ts the grand pillar that supports this barrel -shaped 

Give in full the illustration of breatliing presented in Figs. 27 and 28 



RESPIRATION. 



5'J 



iVamework. The ribs cc c are fastened very strongly 
by ligaments to the spinal column. They are twenty- 
tour in number, twelve on each side. They extend 
round towards the breast-bone a^ in front. 

11. The ribs do not join directly to the breast-bone, 
as you can see in the Figure. There are pieces ol 
cartilage, or gristle, as it is commonly called, that 
connect them to the breast-bone. The object of this 
is plain. If the ribs extended to the breast-bone, 
they would break very easily, if they w^ere struck. 
But the cartilages give a little, as it is expressed, when- 
ever the chest receives a blow, and so the ribs aro 
sieMom broken. 

Fig. 30. 




Describe U»<^ framework of the cbest. How many ribs are there } 
Hew are tb^ rihs coDDected with the breast-bone ? What is the object 
vf thin p,r»*aui»emeLt? 



60 



FIRST BOOK IN PHYSIOLOGY. 



12. This framework of the chest is connected 
together, as I have ah^eady said, chiefly by muscles 
It is these muscles that work the chest in the move- 
ments of breathing. The principal muscle that acts 
in breathing is called the diajphragm. It is a stout 
muscular and tendinous sheet, extending across the 
lower part of the chest. It is the wall that separates 
the cavity of the chest from the cavity of the abdo- 
men. Above it are the heart and the lungs, and 
below it are the stomach, the liver, the intestines, <kc. 
It is represented in Fig. 30. Here you have the cav- 
ity of the chest, c^ laid open, the ribs being cut 
away in front, and the heart and lungs taken out ; D D 
is the diaphragm. It is fastened to the spinal column 
behind, to the breast-bone in front, and to the lov/er 
ribs all around the sides. You see that it is not flat. 
^^®- ^^- but is arched upward. 

13. I will now show you 
how the diaphragm acts in 
respiration. You can see that 
if the tibres of the diaphragm 
contract or shorten them- 
selves, it will not be arched 
up so high, and so there will 
be more room in the chest. 
The air, therefore, will rush in 
through the windpipe, just as 
it rushes into the bellows wlien 
you move the handles apart. 
This I will make clear to yon 




How is the framewoik of the chest connecte \ together ? Describe 
the diaphragm ? Whit are above aod what are below it ? To what is 
it fastened ? What is its shape ? 



KESPIRATION. «) 

by Fig. 31. Let a represent the spinai column, h the 
front wall of tlie chest, Co the cavity of the chest, 
and Ca the cavity of the abdomen. At d is repre- 
sented the diapliragm. You see that if the fibres o( 
the diaphragm are shortened, so as to flatten its arch 
down to the line 6, the room in the chest will be very 
much increased. This is what takes place every 
tune that you make an inspiration or draw in a breath 
When, on the contrary, you make an expiration, or 
force out the breath, the diaphragm is pushed upward, 
as at d^ and so the room in the chest is lessened. 

14. If when you draw your breath in, you will 
place your hand on the abdomen, you will perceive 
that it presses outward. This is because, as the arch 
of the diaphragm is flattened in inspiration, the con- 
tents of the abdomen are all pressed down by it. But 
when you force out the breath from the lungs the 
abdomen moves inward. For in expiration, the stom- 
ach, liver, (fee, are moved upward, and they push 
up the arch of the diaphragm. 

15. Commonly the diaphragm does most of the 
work in breathing. But there are other muscles that 
assist a little general!}', and sometimes assist very 
much. They are muscles that move the whole frame- 
work of the ribs and the breast-bone forward and 
upward. By doing this they enlarge the room in the 
chest in front and at the sides at the same time that 
the diaphragm does below. Whenever you see the 



Dc'sci'ibe by Fig. 31 the manner in wliieb tbe dijjpbi-ngm acts. Wliy 
does tbe abdomen move oiitwai'd in inspiration and inward in expini- 
tion? Wbal musMes issist in breathing? Do tbese muscles act much 
"•rdirarily ? 



^i FIRST BOOK 1]S^ rillSiOLOGY. 

chest heaving from severe exercise, or from clifficulfj 
of breathing, m disease, these muscles are acting 
strongly, moving the ribs and tlie breast-bone upward 
and forward. 

16. I said in the first part of this chapter, § 3, 
that the dark blood that comes to the lungs is changed 
to red blood in the air-cells. And you can see, from 
what you have learned in this and in the last chapter, 
how important it is that this change in the blood 
should be well and thoroughly accomplished. If the 
blood is not changed at all, death results at once ; for 
the dark blood is a deadl}^ poison to all the organs, if 
it goes to them in the arteries and gets into the capil- 
laries. Life cannot go on without red blood is con- 
tinually sent to the organs. This is the reason that 
life is so soon destroyed in drowning. No air can get 
into the lungs, and the air that is there is soon used 
lip. The blood that comes to the lungs verj^ soon 
therefore ceases to be chanored, and so dark blood 
goes to the brain and all the other organs, the ma 
chinery all stops, and life ceases. 

17. Life is destroyed in drowning, then, in the same 
way that it is when a cord is tied tightly around the 
throat. It is destroyed by keeping the air from going 
mto the lungs, and not by having w^ater get into them, 
as is very commonly supposed. Disease often produ- 
ces death by keeping the air from getting freely 
into the air-cells of the lungs. The disease called 
croup, sometimes so blocks up the windpipe that 



Why is it fo importaut that the dark blood should be changed to red 
in the lungs 5 How is life destroyed in drowning? How does diseas* 
often produce de^.th ? 



U E S P I K A. T 1 N . t)3 



\' 



ei-y little air can get tlirough it into the lungs, and 
so it destroys life, because the blood cannot be 
chang'ed anything: like as much as is needed. 

18. Life has been sometimes destroyed by confining 
too many persons together in one apartment. The 
difficulty liere is really the same as in drowning. It 
is the want of air. Death occurs, because from the 
want of air the blood ceases to be changed in thf^ 
lungs. I could cite many interesting cases of this 
character, but I will give you but one. A ship, 
called the Londonderry, had a large number of emi- 
grants on board. A storm arose, and all the passen- 
gers were ordered to go below. They were very 
much crowded, and all the air which they breathed 
came to them through the hatchway, an opening in. 
the deck. But as the sea dashed over the vessel, the 
water poured down this opening. The captain, there- 
fore, had a tarpaulin (a cloth through which neither 
water nor air can pass) nailed over it. The result was 
that a large number of the emigrants died for want 
of air. Their cries of distress could not be heard from 
the noise of the storm, but a strong man at length 
forced a hole tlirough the tarpaulin, and told the cap- 
tain that the people were dying. The tarpaulin w^a^s 
torn off, and thus many of them were saved. 

19. If fresh air is so absolutely necessary to life, 
tnen the health of the body must be injured, when, 
from day to day, the lungs do not breathe enough of it 
One sometimes feels very languid in a crowded assem- 

Wbat is said of death being sometimes produced by a want of ventil- 
ation? Relate the case stated. How is the health injured by deficient 
wf^utilation, suffered from day to day ? 



t>4 FIJIST BOOK O PHYSIOLOGY. 

bly. This is because enough good fresh air does not 
get into the lungs, and the work of changing the 
blood in them is therefore not well done. Now if 
this work is poorly done in the lungs every day, the 
blood, the building material of the body, will not be 
as good as if the lungs did their work well. The con- 
sequence will be that the building and the repairing 
will be poorly done. In other words, the body will 
not be vigorous, and will be liable to disease. Living 
in small or crowded apartments often does much 
hay ai in this way. 

20. There is another way besides those that I havt 
mentioned, in which the air can be prevented fronc 
getting to the lungs. The air-passages may all be 
open, and there may be plenty of air, but if the 
muscles of the chest cannot act, no air can go into the 
lungs through the windpipe. The air, you remember, 
goes in only because the space in the chest is enlarged 
by these muscles. If then these muscles are in any 
way prevented from acting, the air will be kept out 
from the langs, and the person will die for want ol 
air, just as he does when water or anything else shuts 
up the passages to the lungs. 

21. Life is not very often destroyed in this way. It 
IS sometimes, however, and I have already alluded in 
this chapter to a case of this kind. I mean the case 
spoken of in § 6, of a man with a bank of earth fallen 
upon him. In such a case death is caused very much 
in the same way that it is in drowning. In both 
cases air is prevented from getting into the lungs, 

What happens if the muscles of the chest cannot act f How dt>eg 
death occur in such a ease ? 



RESPIRATION. 6& 

though in a different way in each ; the blood is there 
fore not changed from dark to red ; dark blood goes 
to the organs of the body ; these organs stop work, 
for want of red blood, and life therefore ceases. 

22. Though life is not often destroyed suddenly by 
pressure on the chest, it is in many cases destroyed 
gradually by this pressure. A great pressure, as you 
have seen, causes death at once, by keeping out the 
air entirely ; but a small pressure prevents the lungs 
from getting as much air as is needed, and, although 
this does but little harm at any one moment, by being 
continued a long time it will injure the health and 
shorten life. 

23. That you may understand just how this contin- 
ued small pressure does harm, call to mind the way 
in which the blood is changed in tlie lungs. It is 
done, as I told you in §3, in the air-cells. Each one 
of these cells has to do its share of the work. It must 
change the blood that comes to it. And that it may 
do this, the air must go in and out of it freely. But 
this cannot be if the chest cannot be well expanded 
Pressure on it will keep the air from going as freely 
into the cells as it should, and so the blood cannot be 
as thoroughly changed as is necessary to make it good 
material for building and repairing. The blood is 
poor blood, and therefore the vigor of the body is 
lessened and the health is injured. 

24. Continued pressure around the chest does harm 
in another way also. The lungs, like any other ma- 
chinery, cannot keep in good condition unless they 

'Vhat effect is produced by a small but long-coDtit ued pressure on tb* 
ehost ? Explain how this effect is produced 



t56 FIRST BOOK IN PHYSIOLOGY 



work fjeely. If tliey are continually pressed upon, 
80 that they cannot expand freely as they take in the 
air, the tubes and cells get clogged here and there 
from time to time. The difficulty is not noticed per- 
haps for a long time, but at length the lungs become 
manifestly diseased. You see, then, that a continued 
pressure of the chest does harm in two ways. 1st, It 
does harm to the whole body, because it makes the 
blood poor. 2d, It does special harm to the lungs 
themselves. 

25. If the chest is pressed continually while the 
lungs are growing, they will not be large enough to 
do the work that is needed. You have seen that in 
the building and repairing of the body the digestive 
machinery, the circulating machinery, and the ma- 
chinery of the respiration, each has its own work to 
do. Now if any one of these sets of machinery is 
cramped and small, it will not do its share of the work 
well, and the body will be poorly built. When the 
ciiest is pressed upon during the growth of the body, 
the breathing machinery is cramped and is made 
small. There are not air-cells enough to change all 
the blood that the body needs as it grows. It there 
fore will not grow well. It will not be strong. 

26. The chest is often much pressed by tight 
clothing while the body is growing. The lungs are 
in this way made to be very much smaller than they 
should be. In Figs. 32 and 33 you see this illustrated. 
In Fig. 33 is represented the chest of its natural size. 



In wbat two ways does piessure on the chest do harm? What 
happens if the chest is pressed continually during the growth of the 
hod\ ? 



RESPIRATION. 



^1 



Fio. 32. 



Fig. 33. 





In Fig. 82 you see the chest as it is in one that has 
been girt round tightly all her life, so as to make her 
waist very small. The ribs, you see, are brought 
verj^ near together, so that they could hold only very 
small lungs. Health and vigor cannot exist with 
such small breathing machinery. They are sacrificed 
in such cases for the sake of a small waist. 

27. In China, instead of a small waist, a small foot 
is considered very desirable in a female. The foot is, 
therefore, put under pressure while it is growing, just 
as the chest often is among us. And it is astonishing 
how small and into what a shape it can be made to 
Fig. 34. Fig. 35. grow. In Fig. 34 is a side 

view of a Chinese lady's foot. 
In Fig. 35 is a view of the 
sole of the same foot. You 
see that all the toes but the 
great one are turned in under 
the foot. We laugh at the folly of the Chinese, but 
the folly of one that cramps the chest, as represented 




Compare tlie compression of the chest with the compression of the 
ftjet as practiced in Chinj*- 



68 FIRST BOOK iN PHYSIOLOGY. 



in Fig. 33, is greater, because the liiDgs are mur.V 
more imj>ort£^.nt organs than the feet. 

28. I have told you that the blood is changed in 
the lungs from a dark to a red color. Tou have been 
perhaps curious to know what other change takes 
place in it at the same time. It is very much changed 
in its co7nposit{on. And the air in changing the blood 
is changed itself. The air that yon breathe out is not 
the same as that which you breathe in. When you 
breathe in, it is fresh air that goes into the lungs ; 
but when you breathe out, the air that comes from 
your lungs is partly a gas or air, called carbonic acid 
gas. This gas you cannot live in as you do in the air 
that is all around you. No animal can live in it. 

29. If you should put a bird into a jar, and cover it 
over with a bladder tightly, so that no air can get in 
or out, the bird would breathe a little while and then 
would die. The explanation is this : The bird uses 
up the air in the jar, and the carbonic acid gas which 
he breathes out takes the place of the air. So it was 
with the passengers in the cabin of the Londonderry, 
mentioned in § 18. The cabin, with the tarpaulin 
nailed down over the hatchway, was to them as the 
jar with the bladder tied over it is to the bird. They, 
like the bird, used up the air, and the carbonic acid 
gas which they breathed out from their lungs, took its 
place in the cabin, as the carbonic acid gas from the 
lungs of the bird takes the place of the air in the jar. 

30. This carbonic acid gas is carbon or charcoal 



What is said of the change of the blood in the lungs ? VVhat is the 
difference between the air that you breathe in, and that which yew 
l-reathe out? Explain the experiment with the bird. 



RESPIRATION. 



69 



united with a gas called oxygen. The amount of tliis 
carbonic acid gas that you breathe out from your 
lungs in the course of a day is such that it contains 
several ounces of charcoal. This gas comes from the 
blood in the lungs as it changes from dark to red 
blood. At the same time a part of the air that wA 
breathe in is united with the blood. The air is com- 
posed of two gases, called oxygen and nitrogen. It 
is the oxygen that unites with the blood. 

31. You see, then, that a sort of exchange is made 
in the lungs. The blood comes there from all parts 
of the body full of carbonic acid gas. This it lets out 
in all the air-cells, so that it can be breathed out 
through the windpipe. At the same time that it lets 
out this gas it takes in a supply of oxygen. It is this 
exchange of carbonic acid gas for oxygen that alters 
the blood from dark to red blood, and thus fits it t(» 
be used again in nourishing the body. 

32. As all animals are throwing ofi* from their lungs 
carbonic acid gas, and are taking oxygen into the 
blood, one would suppose that the oxygen in the air 
would all be used aip, and that we should have car- 
bonic acid gas everywhere in its place. How is it 
that it is not so ? I will tell you. The carbonic acid 
gas is all taken away by the leaves, which are the 
lungs of plants. At the same time the leaves, give 
out oxygen. The leaves then do just the opposite to 
what our lungs do. They discharge oxygen and take 
in carbonic acid gas, but our lungs discharge carbonic 

What is the carbonic acid gas breathed out made of? From what 
does it come ? What part of the air unites with the hlood ? What ia 
the exchange made in the lungs ? What is the effect of this exchange f 



70 FIRST BOOK IN PHYSIOLOGY. 

acid gas and take in oxygen. An exchange, then, is 
constantly going on betweeu onr lungs and the le ives. 
Our lungs give them carbonic acid gas, and they give 
our lungs oxygen. 

33. The lungs vary much in different kinds of aai- 
raals. The gills of the fish are its lungs. But how, 
you will ask, does the fish get the air to his luhgs 
while he is in the water ? 1 will tell you. There is 
always some air in the water, and the air is made to 
act upon the blood in the fish's gills in this way : The 
fish makes the water run through his mouth, and then 
out through the feather-sliaped gills. And as the 
water is passing out through them, the air in it 
changes the blood in the fine blood-vessels spread out 
there, just as the air in the air-cells of our lungs acts 
on the blood in the blood-vessels that are in them. 
The fish then may be said to breathe air and water 
together. We cannot do this, because our lungs are 
not fitted, as the lungs or gills of the fish are, to sepa- 
rate the air from the water. We should be drowneci 
if we should try to do it. And, on the other hand, 
the fish dies when he is taken out of the water, be- 
cause his lungs are not fitted, as ours are, to use air 
alone. He must have his air mixed up with water, 
or it is of no use to him. 

34. It can be proved by experiment that it is the 
air in the water that keeps the fish alive. If a fish 
be put into a glass vessel filled with water, and covered 
with a bladder tied over it, so as to make it air-tight, 



Describe the exchange that takes place between the Inngs of animals 
and the leaves of plants. What are the lungs of fishes ? How do they 
uso them ? Why cannot fishes breathe air alone ? 



RESPIRATIv)N. 7] 



the fisli will hoou die, because it will soon use up ai. 
the air that is in that little quantity of water. When 
we speak, then, of fishes living in water, it is not 
Btrictly true — they live in water that has air mixed 
with it. 

35. The lungs of insects are mere air-vessels here 
and there in different parts of the body. You can see 
the holes opening into them on the sides of the insect. 
The grasshopper has twenty-four of these holes in 
four rows. 

36. There is a curious arrangement of the breath- 
ing machinery in birds. They have sacs or bags in 
different parts of the body that are connected by tubes 
with the lungs. These they make use of in flying. 
When they wish to fly upward, the lighter they make 
themselves the better. They therefore force air froip 
the lungs into these sacs. But when they wish t( 
come down quickly they let the air out of the sacs. 
Birds that fly very high, or are long upon the wing, 
have many of these sacs, and even some of the bones 
are made in them so that they can hold aii*. 

37. The chief use of the machinery of the respira- 
tion is, as you have seen in this chapter, to bring the 
air to the blood in the lungs, that it may purify it and 
fit it to be used again. But the Creator almost always 
makes a thing useful in other ways besides the use 
for which it is particularly designed. This is true of 
the respiration. This is made use of in man and in 
many other animals for the production of the voice. 

How can you prove that it is the air in the water that keeps fishea 
alive? What are the lungs of insects? What peculiarities are ther« 
in the breathing apparatus of birds ? WHiat is the chief use of tlie ret* 
piratioD ? What i8 another use of the respiration T 



72 FIRST BOOK IN PHYSIOLOGY. 

38. The breathing machinery, then, besides being 
a chemical laboratory for changing the blood, is also 
a musical instrument. I will speak of the different 
parts of this instrument. You feel in the upper part 
of your throat, in front, a firm body, the larynx, com- 
monly called Adam's-apple. This is the music-box of 
the instrument; that is, it is the place where the 
voice is made whenever you speak or sing. The chest 
is the bellows to this little organ in the throat. It 
holds the air in its lungs, and blows it out through 
the windpipe into this music-box to make the voice. 

89. The voice is made in the larynx very much as 
sounds are made in other musical instruments. It has 
two flat cords stretching across it, and the air comes 
out between them. When you force out the air from 
the lungs, it strikes on these cords and a sound is made, 
just as when you blow on a clarionet the air from 
your mouth makes the sound by striking on the reed. 
It is the vibration or shaking of the cords by the air 
tliat makes the sound of your voice. You can see 
this vibration in some instruments as they are played 
upon. You can see it in the strings of a violin as the 
player draws the bow across them. And the air does 
to the cords of the music-box in your throat the 
same thing that the bow does to the violin. It makes 
them vibrate. You can see this vibration, also, if you 
look into a piano while some one is playing on it, and 
observe the strings as they are struck by the keys. 

40. The air is passing out and in through the chink 

Describe the apparatus of the voice. How is the "^oice made! 
Trace the resembhmce between the apparatus of the voice and inusie&l 
iustruments. 



KESPIRATION. 



between the cords of tlie larynx continually as you 
breathe. But it does not, as you know, ahvays pi!)- 
duce a sound. I will explain to you why it is thai a 
sound is sometimes made as the air passes through 
this chink, and sometimes is not. When the cords 
are loose they do not make any sound. They are 
loose when you merely breathe. But when you speak 
or sing, they are tightened. You know that the strings 
of a violin must be stretched tight, or they will give 
no sound. And so it is w^ith the cords of your larynx. 
When you whisjoer, these cords are loose, and the air 
goes quietly by them, and the sound is made by the 
mouth and lips. In W'histling, also, they are loose, 
and the sound is produced by the air as it passes 
through the lips. 

41. There are little muscles that tighten the cords 
of the music-box in your throat when it is needed. 
When you are merely breathing, these muscles do not 
act. But w^ien you speak or sing, they contract, and 
thus tighten the cords. The different notes of the 
sound depend upon the degree to which these cords 
are tightened. When the note is a high one, they are 
tightened very much; but when the note is a low- 
one, they are tightened but little. The working of the 
little muscles in tightening these cords is regulated 
by the mind in the brain, by means of the nerves that 
go to them, 

42. It is only animals that live in the air that have 
a voice. Fishes have none. Some animals can live 



Why does not the air always produce a sound as it goes back and 
forth through the cords of the larynx? By what are the cords of tho 
larynx tightened ? How are the different notes of the voice uroduced 8 
4 



74 FIRST BOOK IIS PHYSIOLOGY 

both in the water and in the air. This is the case 
with frogs. If you watch a frog, you will see that he 
makes no noise while under water, but he does all his 
croaking when he puts his head up into the air. 

43. Man is the only animal that can talk to any 
extent with his voice. He does it in this way : The 
sound, being made in the larynx, is put into various 
shapes, as we may saj^ as it comes out through the 
mouth. The palate, the tongue, the teeth, the lips, 
&c., give it these various shapes. This is what i« 
called the arUmilation of the voice. 



CHAPTEE VI. 

BUILDING AND REPAIRING. 

1. We are so accustomed to see plants and animals 
grow^ that we do not think of the wonderful processes 
by which growth is effected. We get the idea in our 
childhood, that growth is a very simple thing. But 
it is not so. It is very complicated, and there are 
many things about it that are very mysterious. 

2. Everything which grows is made. Growing is 
building. There must be, therefore, something to 
build with — that is, a building material. In plants, ^ 
the sap is the building material ; and in animals, it is 
the blood. Every part of the human body is hidlt , 
and, as you will see in this chapter, there are every 

What animals have a voice ? What is the articulation of the \oi«3e 
Is growth a simple process? What is growing? What is the build 
ing matei^ial in plants, and w^hat in animals? 



BUILDING AND REPAIRING. 75 

where little builders, that are always at work in 
building or in repairing. 

3. All the various structures of the body are made 
or built from the same thing, the blood. This ap- 
pears very wonderful, when we observe how different 
from each other some of these structures are. For 
example, how different are the white hard teeth from 
the soft red gums that surround them, and yet both 
are made from the blood. 

4. That you may see how great is the variety of the 
^structures formed out of the blood, I will direct 
your attention to some one part of the body. Look, 
for example, at the eye. Observe how many and 
how various are its parts. I will mention most of 
them. They are, the bony socket ; the eye-lids ; the 
eye-lashes ; the firm white coat of the eye ; the clear 
round window in front ; the beautiful iris ; the three 
different fluids that are in the eye-ball ; the muscles 
that move the eye; the cushion of fat in which it 
rests; the nerves; the tear-gland, &c. All these 
parts, so different from each other, are made from 
the blood. And so it is with all the different parts 
in every portion of the body. 

5. Not only are all the structures of the body buiit 
from the blood, but the vessels that carry the blood 
to them, and the heart that pumps it into them, are 
made from the blood that they contain. This is not 
less wonderful than it w^ould be to have the pipes oi 
an aqueduct made out of the water that is in them. 

From what are all the different structures in our bodies formed ? Il- 
lustrate the variety of structures made from the blood by the parte of 
Uie eye. What is said of the blood-vessels and the heart ? 



b FIRST BOOK IN PHYSlOLOGy 

6. The fluids of the body, as well as its structure?, 
are made from the blood. The glands that secrete 
these fluids make them from the blood that flows 
through them. Thus the tear-glands make the tears 
that moisten the eye from the blood. The liver 
makes the bitter yellow bile from the blood also. 
And so of the rest of the glands. Observe, that the 
glands are made from the same blood from w4iich 
their secretions are formed. Thus the tear-gland and 
the tears are made from the same blood. That is, the 
factory is built with the very material from w^hich it 
manufactures its product. 

7. Tou can see better how wonderful it is that all 
the parts of the body are made from one common 
building material, if I compare the building of the 
body to the building of a house. When a house is 
built, there must be gathered together a great variety 
of materials. There must be beams, boards, shingles, 
&c., and nails to fasten them together. There must 
be bricks made of clay. Lime must be obtained from 
one place, sand from another, and hair from another; 
and these mixed make the mortar to fasten the bricks 
together. There must be stone for steps and founda- 
tion, and various other purposes. Glass must be 
obtained for the windows, and paper for the w^alls. 
A variety of materials is required, to make paints of 
different colors. All these and various other things 
must be collected, to build a house. And then, to 
finish the house after it is built, materials are needed 



What is said of the fluids and the glands that secrete them ? Give 
ttie comparison between the building of the body and the building of a 
I'ouse, 



BUILDING AND ilP^PAIRING. 1 

from every (quarter, to provide the various article of 
furniture, as carpets, chairs, sofas, beds, bureaus, r"jir- 
rors, lamps, &c. 

8. Now, in the house which your spirit inhabits, 
the bodj^, there is a much greater variety of structure 
and furniture than there is in the houses that man 
builds ; and yet all of it is built of the same material. 
Many of its parts dilier from each other much more 
than the different parts of a house. It would be pass- 
ing wonderful if bricks and boards and nails were 
made out of the same thing, but these articles are not 
so much unlike each other as the hair, the skin, and 
the teeth. Some of the parts of the body are totally 
unlike the blood, and it seems impossible that they can 
be made from it. It would seem comparati yely easy 
to make the red muscles out of the blood, but it is 
not so with such structures as teeth, nails, tendons, 
hair, ifec. 

9. I will now show you how the blood is used as the 
building material of the body, and what are the work* 
men that thus use it. The blood is not used for building 
and repairing while it is in the arteries, nor while it is in 
the veins, but only while it is inpithe capillaries. The 
heart sends it through the arteries to the capillaries, 
that it may be used there. Then, after it is used, it 
goes back to the heart through the veins. The heart, 
and the arteries, and the veins are therefore simply 
an apparatus or set of machinery for circulatii^g the 
building material. This apparatus may be called the 



"What is said of the differeaee between the structui'es of the body ar^ 
the blood from which they are made ? Where is the blood when it ' 
aped for building? What is sa'4 of the npparatus of the circulation I 



78 FIRST BOOK IN PHYSIOLOGY. 

common carrier of the body. It carries the building 
material to the very door, as we may say, of all the 
little builders everywhere. 

10. It is supposed that the building is not done by 
the capillaries tliemselves. These merely hold the 
blood, while some other small vessels, called forma- 
tive vessels, use it to build with. These formative 
vessels have the power of selecting from the blood, 
while it is passing through the capillaries, just what 
they need to make the different structures. Some are 
bone-makers, some nerve-makers, some skin-makers, 
&c. The bone-makers select from the blood what is 
needed to make bone, the nerve-makers what is 
needed to make nerve ; and so of all the various tex- 
tures of the body. 

11. Sometimes the formative vessels fail to make 
the right selection, as for example, when bone is formed 
where it should not be. Thus, sometimes in aged 
persons, the arteries become here and there bony. 
In this case some of the artery-makers leave off their 
u>iuil business and go to making bone. Sometimes 
even the valve-makers in the heart do this. When 
warts appear upoD»the skin it is because the skin- 
makers at those places leave off their regular business, 
and make something else. But such irregularities are 
not common. Generally, the formative vessels very 
faithfully adhere to their regular woik, as we may 
express i% and choose just the right material from the 
blood, as it passes along by them in the capillaries. 

By what vessels is the building of the body done ? What is said ol 
the seiecting power of these -^'essels ? Ulustrate the fact that they 
sometimes eir in theij' selection. 



BIMLDING AND REPAIRING. 79 

12. Each set of formative vessels appear to work 
together, as if there was some kind of agreement 
between them. If there w^ere not this concert of 
action there would be confusion. The different parts 
would not be properly formed. If there was irregu- 
larity, for example, among the bone-makers, the 
bones would not be regularly made. There w^ould be 
bunches, and sharp points, and rough places, where 
there is now smoothness and regularity. 

13. This concert or agreement of action in the foi- 
mative vessels, is seen in the different shapes that the 
same kind of structure takes in different parts of the 
body. Thus, every bone differs in shape from every 
other bone. That is, every set of bone-makers have a 
plan of their own, which is different from the plan of 
every other set. For example, the bone-makers that 
make the knee-pan have a very different plan from 
another set in the same neighborhood that make the 
long thigh-bone. So also the makers of any muscle 
have a different plan from the makers of any other 
muscle. And so of other kinds of structures. The 
formative vessels everywhere act upon some regulai 
fixed plan, just as if they thought it out, and agreed 
together as to what they would do. 

14. This concert of action is so perfect in each set 
of the formative vessels, that the diflerent sets do not 
ijiterfere with each other when working in the same 
neighborhood. Each set keeps at work commonly 
within its own bounds, and does not encroach upon the 



What would result if there were not a concert of action among th€ 
formative vessels? How is this concert of action seen in th<5 flifferenl 
fthapen given to the same kind of structure? 



so FIRST BOOK IN PHYSIOLOGY. 

work of another set. Thus the tooth-makers and the 
gnm-makers never interfere with each other. There 
are, as you have seen, many different structures in tlie 
eye, but there is no interference between the different 
sets of workmen in constructing the eye and in keep- 
ing it in repair. The builders, for example, that con- 
struct the white part of the eye-ball never encroach 
upon those that make the clear window in front, that 
fits into the white part, as the crystal of a watch does 
into the case. They only build up to the edge of this 
window all around, as if they agreed to build along 
this circular line. 

15. You can see this concert of action very curiously 
exhibited in the formation of the lips. I told you in 
chapter II, § 20, that the red covering of the lips is 
somewhat like both the skin and the mucous mem- 
brane that lines the mouth, and yet it differs from 
either of them. The lip-makers then are between 
two sets of workmen, that are making textures some- 
what similar, and yet they keep their work very dis- 
tinct from that of the workmen on either side. They 
are always making the red delicate texture of the lip, 
and never go to making skin with the skin-makers on 
the one side, or mucous membrane, with the work- 
men on the other. 

16. This concert of action in the formative vesseJb 
is beautifully shown in the increase of the size of the 
different parts of the body, as the child grows up to 
manhood. All the different structures in any part 



How ie concert of netion seen in the fact that the different jets of foi-- 
inative vessels never interfere with each other? Give tlie illustration 
•Ji re.^ard t<> thr lips. 



BUILDING AJSD REPAIRING. Si 

keep the same propoitions as ihej increase in size. 
For example, as the tinger of the child grows to be 
the large linger of the adult, all the different sets of 
buihlers do just the right amonnt of building. The 
nail-makers make just enough nail, the skin-makers 
enough skin, the bone-makers enough bone, &c. II 
the builders did not work after some plan, there would 
be too much of one structure and too little of another, 
and the finger of the man would not be like the finger 
v>f the child. And so of other parts. 

17. There is another thing to be noticed about this 
agreement of action in building t)ie body. There are 
two halves of the body, which are generally just alike 
The right hand is like the left, the right side of the 
face is like the left, and so of the other parts. That" 
is, for every set of builders on one side of the body 
there is another set on the other side, working after 
precisely the same plan, as if they had agreed to do 
so. Sometimes this agreement is not fully carried 
out, and one part is not shaped exactly like its corres- 
ponding part on the other side. Thus, the two sets 
}f nose-makers in tlie two halves of this organ some- 
times do not work exactly after the same pattern, and 
there is some irregularity, perhaps one-sidedness 

18. What I have just said of the bod)^, as being made 
of two halves just alike, is not true of all the organs 
within the body. While the brain has two halves just 
alike, this is not true, as you have already seen, of the 
lungs, the heart, the stomach, the liver, &c. But each 



How is the concert of action in the formative vessels seen in tlm 
regular growth of the body? How is it seen in the two halves of ths 
l'>orly ? Is the coneert al^'nvs pf-ifpct ^ 
4-^ 



S2 ^IRST BOOK II\ PHYSlOLOGr. 

of these organs is constructed after a fixed plai) of its 
own, and the formative vessels, in constructing it 
after this plan, must have an agreement in their ope- 
ration. 

19. From all that I have said in the last few para- 
graphs, it appears that there is as much agreement of 
action among the formative vessels of the body, as 
there would be if they w^ere intelligent workmen, and 
worked under directing leaders. In what way the 
Creator makes them to work together thus, we do not 
understand. 

20. There is not only building going on in every 
part of the body, but there is repairing also. And 
they go on together. You remember that I said in 
the first chapter, that the machinery of the body is in 
use all the time that it is building, or ratlier all the 
time that it is changing from small machinery into 
large machinery. There is therefore some wear from 
this use, and hence repairing is needed all the time. 

21. The way in w^hich the repairing is done is this. 
When any particles in any part become useless, they 
are taken out of the way, and are carried off in the 
dark blood. At the same time the formative vessels 
:ake new particles from the red blood in the capilla- 
ries, and put tliem in the place of those that are 
removed. As you work the muscles, some of the par- 
ticles get worn out and useless, and so they are carried 
ofi', and new particles are put in their places. Ah 
your mind uses the brain in thinking and studying, it 

W^hat organs of the body do not have two halves uist alike ? Ho^ 
IS 30Dcert of action shown in constriictins^ them ? Do we know how this 
eoncert of actioD in the formative vessels is prochiced ? What is Baid 
t'f the repairing ^f the body ? 



lUMJ.DING AND REPAIRING. ^^'5 

wears out some of the particles there, and they are 
taken away, and new ones are supplied. And so of 
'>ther parts of the body. 

21. In this way there is a change going on continu- 
ally in all parts of the body. There are probably 
scarcely any particles in your body now that were 
there when you was born. It is a very common no- 
tion that the whole body changes once in seven years. 
But this is not so. There is no such regular period 
for the change. As long as any particle is useful in 
its place it remains there ; but when it becomes use- 
less it is taken up and carried away. 

22. The change is more rapid at some times than 
it is at others. You know how very fast sick persons 
sometimes become thin, and then how fast they gain 
flesh when they begin to eat again. In such cases a 
large portion of the body is entirely changed in a 
very short time. The change in young children is 
sometimes very great. They become so poor in a lit 
tie time that the loose skin hangs upon their limbs like 
clothes ; and then when the disease is gone, and the 
appetite returns, the limbs soon become plump again. 
jN^ow the changes which you see so plainly in such 
cases are going on all the time sh^wly and quietly in 
the body. Old useless particles are constantly taken 
away, and new particles put in their places. 

23. It is to effect these constant changes in the 
growth and repair of the body that the blood is m 
motion everywhere. If these changes were not going 

Describe the way in which the repairing is done. What is said c ' 
Ihe change that is occurring in all parts of the body ? Is this chan^ 
jjoing on always just alike ? In what oases is it very lapid ? 



84 FIRST BOOK IN PHYSIOLOO^. 

on, there would be no need of having the blood 
circulate. In some animals these changes are stopped 
in cold weather, and the blood stops moving. Great 
multitudes of such animals as frogs, bats, flies, spiders, 
ifec, go into retirement in the autumn to sleep through 
the winter. Their bodies remain without change all 
this time. They are alive, but as still as death. The 
machinery of life is still, and so there is no wear and 
tear. There is therefore no repairing to be done, and 
so there is no need of having the blood circulate. And 
as there is no circulation there is no need of respira- 
tion. 

24. When the warm weather comes, these animals 
wake up from this state of torpor. The blood begins 
to move again, and they breathe, so that the air can 
go into the lungs and change the blood. They begin 
to eat, too, so that some new blood can be made. A 
gentleman who was curious on this subject, kept some 
frogs and snakes in this torpid state in an ice-house for 
three years and a half, and then revived them by 
bringing them out into the warm air. 

25. I have said that the useless particles that come 
from the wear and tear of the organs in their daily 
use are taken up to be carried away in the dark blood. 
I will now show you how this waste matter is disposed 
of. There are various ways of carrying it off. Some 
of it is discharged by the lungs. At every breath 
some part of the waste matter of our bodies is thrown 
oflf from the lungs in the form of carbonic acid gas, as 

Why is tlie blood coDstantly in motion everywhere ? What is thn 
situation of some animals in winter? What eifoct does the warru 
^^eather of spring produce in them ? 



BUlLDlxVG AND REPAIRINO. 85 

you learned in the chapter on Respiration. Other 
portions of the waste matter are removed by the skia, 
others by the kidneys, others by the liver, &c. 

26. The waste matter is all sent off by these differ- 
ent organs* each doing its share, and in its own way. 
Observe how it is done. The waste matter is in the 
blood. Now as the blood goes to these organs, the 
lungs, the skin, the liver, the kidneys, each does its 
duty in cleansing the blood of the waste matter. And 
in doing this each organ seems to have the power 
of choosing just that part of the waste that it is^ its 
business to throw off. And it never makes a i^is* 
take, and throws off good particles instead of bvid 
ones. But we know that these organs have no thought 
nor knowledge, and therefore cannot choose. A?>d 
the perfect way in which they are made by the Boilder 
of our bodies to do their duty is a mystery which we 
cannot understand. Each organ, I have said. Las its 
own way of getting rid. of the waste matter. F<. r ex- 
ample, it is throu^n off in the lungs in the ail that 
we breathe out, while by the skin it is throwi off 
in a very different form — in the perspiration. 

27. The skin is so important an organ in thi )w- 
ing off the waste of the body, that I will desciibe 
its structure. There are really two skins — a thick 
inner skin, and a thin outer one, called the scarf-skin. 
Tlie coloring matter of the skin is not in the inner 
skin, but in the inner layers of the scarf-skin. When 
the skin is rubbed off, as it is expressed, it is only this 

In what various ways is tlie waste matter of the body disposed of: 
Desciibn tlie mauiier in wliich it is doue. W^bat is said of the sekaina 
power of ihe different organs in G^etting I'id of the waste? Is it tl:;ow»i 
»^1^ in 'he snnie foini from the different cj'irans ? 



^t) FIRST BOOK IN PHYSIOLOGY. 

scarf -skin that is removed, and the inner skin, called 
the true -skin is laid bare. It is the scarf-skin that is 
raised when a blister is applied. 

28. The true-skin is very sensitive, for it has a great 
number of nervous fibres in it. This is for the pur- 
pose of having the skin act as a sentinel for the inner 
organs. If the skin did not, by its nerves, warn of the 
approach of danger, these organs would be much oft- 
ener injured than they now are. The scarf-skin, which 
is not sensitive at all, makes a soft delicate covering for 
the inner sensitive skin. The true-skin, without this 
covering, would look badly, and would feel too keeiilv. 
I shall say something more about the skin as a sensi- 
tive organ in the chapter on the Nervous System. 

29. The perspiration of the skin is in two different 
forms. When the skin feels soft, but does not look 
moist, there is a moisture going from it all the time 
in the form of vapor. This is called insensible per- 
spiration, because we cannot see or feel it. If you 
place your hand, when it appears dry, upon a glass, 
and hold it there for some time, the glass will become 
moist from the insensible perspiration. The skin is 
sometimes covered with moisture, perhaps in drops, 
as, for example, after brisk exercise on a warm day. 
This is called sensible perspiration. 

30. The perspiration is separated from the blood in 
the skin by innumerable little glands. The pores 
through which it is discharged are the outlets of the 

Describe the structure of the skin. Where is the coloring master oi 
the skic ? What is said of the seusitiveness of the skin ? What is the 
use of the scarf-skin ? What is the difference between sensible anu 
msy-nsihle perspiration? By what is the perspiration formed? What 
art ihe poros of the skin ? 



BUILDING AND REPAIRING. 87 

tubes from these glands. There is another set of 
glandii? in the skin that separate an oilj fluid from the 
blood. These oil-factories are most abundant wherever 
tlie skin particularly needs oiling, as at the joints, 
where one part of the skin rubs against another, and 
where the skin is exposed to the air, as in the face. 

31. Tlie skin then serves several diflerent purposes* 
1. It is a firm, but soft and beautiful covering for the 
body. 2. By its nerves it warns of the approach of 
danger. 3. It also, by its nerves, as the organ of 
touch, gives knowledge to the mind of objects around 
us. 4. It discharges, in its perspiration, much of the 
waste matter of the body. 

32. The change that I have described in this chap- 
ter, as going on in all parts of the body, produces to 
a great extent the heat of the body. It does this by 
a kind of combustion or burning. You remember, 
that in the chapter on Respiration I told you that the 
oxygen of the air enters the blood in the lungs, and 
goes with it to the heart, and then is sent, with it, all 
over the body. Now, this oxygen, when it comes to 
the capillaries, is united to carbon, that is, charcoal, 
and makes carbonic acid gas. This gas goes to the 
heart with the dark blood, then is sent with it to the 
lungs, and there is thrown off, as I have already told 
you. At the same time, the oxygen also unites in the 
capillaries wuth another substance, a gas called hydro- 
gen. It is this^ union of the oxygen with the carbor. 
and the hydrogen that makes the heat of tlie body. 

33. Xow this is very much like what takes place in 

What otlier glauds are there in tiie skin, and where are they most 
■iiiiut'i-ous? Mention the four (Jitferciit pui-poses Avhicb the skin selves. 
0i.'80iir)e the ]>roces.? by whieli tlie heat of tlie body is chieflv^ nnxhieed ' 



S8 FIliST BOOK IN PHYSIOLOGY. 

combustion. When we burn charcoal, that is, carbon, 
in the air, it unites with the oxygen of the air; and 
it is this union that makes the heat that is given out. 
So too, when the chemist burns oxygen and liyclrogen 
gas together, it is their union that produces the heat. 
Ho it is in the capillaries of the body. The union of 
tlie oxygen with the carbon and the hydrogen makes 
the heat of the body. There is a fire, then, we may 
say, in every part of the body in the fine blood-ves- 
sels, although there is no flame. 

34r. Carbonic acid gas is produced by the burning 
of charcoal in the air. So also it is produced by the 
fire in the capillaries. It is carried from them with 
the blood to the lungs, and there it is discharged 
through the windpipe. The windpipe may then be 
called the smokepipe or chinmey, through which the 
smoke of this general combustion in the body is let 
oflF into the air. It will be interesting to notice here 
that the w^indpipe answers three diflferent purposes. 
1. It conducts fresh air to the lungs. 2. It carries ofi' 
the bad air^ or, as we may express it, the smoke of 
the fire that is in the body. 3. While carrying ofl 
the bad air it acts, when we speak or sing, as the con- 
ducting pipe of the organ of the voice in the throat 
from the bellows at work below, the chest. 

35. Observe that in this combustion of the capilla- 
ries a part of the fuel is furnished from the waste of 
the body. The carbon and hydrogen that unite with 
the oxygen are, to a great extent, produced by this 
waste. As the oxygen comes in the red blood to the 

Trace the resemblance between this and tlie process of comtuation 
What thiee purposp^^ does the wiudpipe answer? 



BUILDING AND REPAIiUNG. N?» 

capillaries, the useless particles that are to be thrown 
off furnish carbon and hydrogen to be burned with 
the oxygen. And then what results from this burn- 
ing is cari'ied back in the dark blood in the veins. 

36. When anything is burned up it is spoken of as 
being destroj^ed, but this is not so. The burning 
merely changes matter into some other form. Thus, 
when carbon or charcoal is burned in air, the oxygen 
of the air is taken away, and the charcoal disappears. 
But there are ashes left, and a quantity of carbonic 
acid gas has been formefl. So, when oxygen and hy- 
drogen are burned together, they both disappear, but 
in disappearing they form water. The same thing is 
true of the combustion in the body. - The oxygen and 
carbon are burned up together in the capillaries ; but 
carbonic acid gas results, just as when charcoal is 
burned in the air, and this gas is carried'to the lungs, 
to be thrown off through the chimney, the windpipe. 
Oxygen is burned up also with hydrogen in the capil- 
laries, and water results, just as when the chemist 
burns them together. Much of this water tlius form- 
ed is thrown off by the lungs in vapor. It is supposed 
that a man discharges from his lungs in this way 
about two quarts of water in every twenty-four hours 

37. You can see now why it is that exercise in- 
creases the heat of the body. During exercise the 
heart beats quicker than usual, and so sends the blood 
more rapidly everywhere. More blood passes there- 



From what does tbe fuel for the combustion in the body mostly 
come ? Is it sti-ictly correct to speak of a thing as being destroyed^hen 
it is burned ? What are the products of the combustion in the (.'apilla 
ries ? What beconies of these products? 



1)0 FIRST BOOK IN PHrSLOLOGY. 

fore through the lungs. The breathing is quickened 
also, and as more air is taken into the lungs, of course 
.nore of the oxygen of the air unites with the blood. 
But the oxygen is a part of the fuel that is burned in 
the capillaries, and the more fuel there is the greater 
is the heat. The other parts of the fuel, the carbon 
and the hydrogen, are increased also. For these come, 
as I have before told you, from the waste of the sys- 
tem, and there is more wear and tear, and therefore 
more waste, when the body is exercised than when it 
is quiet. 

38. You can see, also, the principal reason that 
some animals are so much warmer than others. You 
have often heard the expression, as cold as a frog. 
The frog belongs to that class of animals that are 
called cold-blooded. These cold-blooded animals 
make but little exertion, and so there is but- little 
w^ear and tear of the system. There is therefore but 
little carbon and hydrogen furnished for the fire in 
the capillaries, and but little heat is made. As there 
is so small a quantity of carbon and hydrogen to be 
burned, there is not mucli oxygen required, and so 
the breathing is performed in a very lazy manner. 

39. If you watch a frog you will see that he exerts 
himself but little in comparison w^ith warm-blooded 
animals, as birds, for example. He never seems to 
take any pleasure in exercise. He never gambols. 
He sits still when he can, and leaps only w4ien he is 
obliged to do it. He does not even croak but seldom. 
But to the bird exertion is a pleasure. He is ever on 

How does exercise increase the heat of the body ? W^hat is the chief 
*?ause of the difference between warm and cold-blooded animals ? 



BUILDING AKD REPAIRING. ^i 

the wing. There is much wear and tear, therefore, in 
his system, and an abundance of carbon and hydro- 
gen is ready to be burned up with the oxygen. His 
blood circulates rapidly, and he breathes quickly in 
order to supply all the oxygen that is needed. And 
the fire which thus burns so briskly in all his capilla- 
ries makes him a warm -bloodecT animal. 

40. A good supply of pure air is necessary to ena- 
ble the system to keep up its heat. The reason is, 
that when the air is impure, there is not a sufiicient 
quantity of oxygen supplied. This part of the fuel 
being deficient, the fire is low, and there is too little 
heat. 

41. The supply of oxygen is often deficient from 
pressure on the chest. Those whose lungs are thus 
prevented from becoming as large as they need to be, 
are therefore much more readily aff'ected by cold than 
those who have chests of the proper size. They 
require more clothing to keep them warm. The . 
heat-making power in them is lessened, because the 
lungs that take in that important part of the fuel, 
oxygen, are not capacious enough. And this lessen- 
ing of the heat-making power of the body is a great 
source of disease. 

42. It is only in a vigorous and active state of tht; 
body that the proper amount of heat is produced. In 
a state of vigor, the blood is rich and is well-charged 
with that important agent of combustion, oxygen. 
And when the body is active, the change that goes on 

Giv3 the comparison made iu relation to the frog. Why is a free 
supply of air necessary to keep up tlie heat of the body? What is saio 
of pressure on the eldest in relation to aniinal heat? 



D2 FlRSl BOOK IN PHYSIOLOGY. 

briskly everywhere supplies the proper quantity >( 
carbon and hj^drogen to be burned \vith the oxygen 
in the capillaries. 

43. The body needs to be well nourished in order 
to maintain its lieat. For its vigor depends to a great 
extent upoa its nourishment. The poorly fed are 
weak, and are easily pinched by the cold. They 
have not enough of carbon and hydrogen and oxygen 
in them to keep up a good fire in the capillaries. 

44. You see, then, that there are three things 
needed to maintain the heat of the bodj^ 1. A full 
supply of fresh air ; 2, sufficient exercise ; and 3, a 
due amount of food. If there be a deficiency of any 
one of these three things the body will be weak and 
easily chilled. 

45. There are some kinds of food that make more 
heat than others, because they contain more carbon 
and hydrogen ; that is, more fuel for burning with 
the oxygen. Animal food, and especially that which 
is oily or fatty, is of this character. This is the rea- 
son that more of this kind of food is needed in winter 
than in summer. It is the reason also that the inhab- 
itants of cold climates eat more meat, and especially 
fat meat, than those who live in warm climates. The 
fat and oil which the Grreenlander devours in such 
quantities are used up as fuel, to k-eep up the heat ot 
the body, in the midst of the intense cold to which it 
is exposed. By eating largely of such food, he can 

Why-are vigor and activity necessary to maintain the animal heat 
properly? What is said <i food? What then are the three things 
needed for the heat of the body ? Are aU kinds of food alike in furnish 
\ng fuel for the auimal heat? What is said of food in relation Ur ^\U 
fercut seasons and different olimates ? 



BUILDING AND REPAIRING. 93 

get along with less clothing than he would otherwise 
require, because it makes so much heat. 

46. The carbon and hydrogen that are burned 
jvith the oxygen, are not furnished wholly from the 
waste particles of the body. Some of this fuel comes 
directly from the food we eat, when the waste doea 
not afford enough of it. Some of it also comes 
irom the fat which is stored up here and there in the 
ceUular membrane of the body. When we are sick, 
and cannot eat, the fat lessens very rapidly, being 
burnt up, as we may say, to keep the body warm. 
So also, when an animal goes into winter-quarters, 
and becomes torpid, or hibernates^ as mentioned in 
§ 23, in this chapter, he is kept warm in this state by 
the fat in the body. He becomes very fat in the 
autumn ; but when he crawls out of his quarters in 
the spring he is very lean, because his fat has been 
burned up, in keeping him warm through the winter. 

47. In this chapter I have shown you what changes 
are going on in the building and repairing of the 
body. You have seen that waste particles are every 
where constantly taken away, and new ones are 
deposited in their places. You have seen that in 
doing this the blood is changed in the capillaries from 
red to dark blood. I have shown you that this is a 
chemical change, and so every little capillary is a 
chemical laboratory. And finally, you have seen 
that there is a fire in each one of these laboratories, 
and that in this way the heat of the body is chiefly 
maintained. 



What tyfo other sources for fuel for the combustion in the body, Rr# 
there besides the waste particles ? G^Ve the suniraai y in § 47. 



94 FIRST BOOK IN PHYSIOLOGY. 



CHAPTER VII. 
THE NERVOUS SYSTEM. 

1. I HAVE thus far told you only about building the 
body and keeping it in repair. You have seen in the 
previous chapters that the blood is the common build 
ing material of the body — that it is the office of the 
digestive machinery to separate from the food the 
nourishing part of it, and fit it to become blood — that 
the circulating machinery circulates the blood every- 
where, that it may be used as building material — that 
the formative vessels, the real builders of the body, 
everywhere use it to build and repair — and that the 
machinery of the respiration keeps the blood fresh 
and in good condition, by continually changing it 
after it has been used by the builders. 

2. Digestion, circulation, respiration, and forma- 
tion, are then all engaged in building and repairing 
machinery. In the remaining chapters of this book 
I intend to explain to you the uses for which this 
machinery is built. 

3. The mind uses this machinery. First, it uses 
some of it to learn what is going on around it. It 
uses the apparatus or machinery of the eye to see 
with ; that of the ear to hear with ; that of the nose 
to smell with; that of the mouth to taste with; and 
that of the skin to feel with. In all these cases the 

Give the summary of subjects treated of in the previous chapters. 
What are to be the subjects of the following chapters as stated in § 2 ? 
What uses the machinery of the body ? For what pi.rpose does th<' 
aiiiid use the machinery of the senses? Ulustrate, 



THE NERVOUS SYSTEM. 95 



mind is acted xipon. Light acts upon it by means of 
the eye ; sounds act upon it by means of tlie ear ; 
odors act upon it by means of the nose, &c. The 
mind is in these 0.2^^^% i)assive. It receives impressions, 

4. But secondly, the mind is in an active state, in 
using some of the machinery of the body. That is, it 
makes impressions upon the world around. It does 
this by moving the muscles. For example, it moves 
the muscles of the voice, and thus produces soundc. 
It works the muscles of the face, to give it expression. 
It sets in motion the muscles of the arm and other 
parts of the body, when we work. 

5. You see, then, that the purpose of all the ma- 
chinery is to have a communication between the 
mind and all that is around it. The mind, by some 
parts of the machinery, makes impressions, and by 
other parts receives impressions. And you see, also, 
that all that goes into the mind gets there by means 
of the machinery of the senses, and all that comes 
out from the mind comes by the machinery of the 
muscles. That is, all the knowledge that enters the 
mind enters by the senses ; and the mind uses this 
knowledge, in acting upon things and beings around 
it, by means of the muscles. 

6. Now the mind makes all this use of the ma- 
chinery of the body by means of the nervous system. 
The brain is the great centre of this system, and hei-e 
the mind has its seat. And the mind is connected 
with the organs of the senses by the nerves that 

Id -what state is the mind in using this machinery ? In usiLg what 
machinery is it in an active state ? Illustrate. What is said of the 
communication between the mind and the world around it ? By nieoQ* 
of whai do3s /.he mind mak^ use of the machinery of the bo<^> ? 



96 FIRST BOOK IN PHYSIOLOGY. 

branch out from the brain, and go to these organs. 
It receives impressions by the nerves that connect the 
brain with the organs of the senses^ and it makes 
impressions by the nerves that go to the muscles, 

7. The brain then may be considered the great 
central workshop of the mind. There it sits and ope- 
rates by the nerves upon all the machinery of the 
body. It receives messages by one set of nerves, and 
sends but messages by another set. The nerves bv 
which it receives messages are called nerves of sen- 
sation. The nerves by which it sends out messages 
are called nerves of motion. You can see how this is 
by a single example. If you put your finger too near 
the fire, you feel pain in it, and instantly draw it 
away. Now see what takes place in this case. The 
sensation made by the fire goes by the nerves of sen- 
sation to the brain, so that the mind feels it ; and 
then the mind sends a message or order by the nerves 
of motion to the muscles of the arm, and they draw 
the finger away. 

8. We know that the nerves are the means of this 
connection between the mind and the various parts 
of the body in this way. If the nerves of any part 
are divided, the part cannot move, and there is no 
feeling in it. For example, if the nerves of the hand 
are divided, you can pinch or prick it without pro- 
ducing any feeling, because the mind has lost its con- 
nection with it. And the muscles of the hand will 
not act if the mind sends a message to them, because 

What is said of the brain ? "What of the nerves of sensation and 
cf motion? Give the ilhistration in §7. How do we know that, the 
nerves are the means of communication between the mind and the dif 
ferent parts of the body ? 



THE NERVOUS SYSTEM. *J^ 

the message can go no further than where the nerves 
are divided, just as when a telegraph wire is broken, 
the electricity can go only to the point where it i? 
l)roken. 

9. The nerves are white cords. Each nerve is 
jiade up of a great number of tubes. These tubes 
are so small that they can be seen only by the aid of 
a very powerful microscope. Each tube is altogether 
by itself. It is never seen to communicate with My 
of the other tubes that are bound up with it in the 
same nerve. Each of these tubes then goes by itself 
from the brain, where it begins, to the place where it 
ends in the body. To every separate fibre of any 
muscle there is probably one of these tubes. This is 
the telegraphic wire by which the fibre is told by the 
mird in the brain to act. As each fibre receives 
a message by itself, whenever the muscle acts, what 
a multitude of messages are sent to the whole muscle ! 

10. Some of the tubes in the nerves are for sensa- 
tion, and others are for transmitting the messages or 
impressions to the muscles. These two kinds of tubes 
are very commonly bound up together in the same 
nerve to go to any part. And yet they are entirely 
separate in their office. For example, in the great 
nerve that goes to the arm, the nervous tubes for the 
muscles and the tubes for sensation are bound up 
together. But as the nerve branches out to be dis 
[ributed, the two kinds of tubes are separated. And 
the same tube never transmits sensation to the brain 
and brings back a message to a fibre or a muscle. 

Of what are the Derves composed Do the tubes in them commuD' 
eate together? What two kiods of tubes are there in tlie nerves? 



J^8 FIRST BOOK IN PHYSIOLOGY. 

The sensation goes by one set of tubes, and the mes- 
sages to the fibres of the muscles come by another set, 

11. In the body and in the limbs the two kinds of 
tubes are bound together in the same nerves. But in 
the face the two kinds of tubes are in two separate 
Bets of nerves. There we have nerves of sensation 
and nerves of motion separate from each other, while 
everywhere else they are mingled together. But 
where they are thus mingled, they are just as sepa- 
rate in their office as where they are in separate 
nerves. 

12. Here, in Fig. 36, is a representation of the 
brain and spinal marrow, with the nerves branching 
out from them in all directions. At a is the cerebrumy 
the upper large brain "filling up a large part of the 
skull, and at h is the cerebellum^ the smaller brain 
lying underneath the cerebrum. You see the spinal 
marrow extending from the brain down the back. It 
is very much like the brain in its structure, and 
should really be considered as an extension of the 
brain itself. You see that nerves branch out from 
the brain and the spinal marrow all over the body. 

13. You observe that the whole of this nervous 
system has two exactly similar halves, just as it is 
with the system of bones, and the system of muscles. 
The cerebrum has two parts just alike, called the 
two hemispheres of the brain. So it is with the cere- 
bellum. There are two sets of nerves also for each 
half of the body that are just alike. 

In what parts of the body are these tubes mingled together in th<j 
same nerves? Where are they in separate nerves? Describe the 
arrangement of the nervous system represented in Fig. 36. Is tho 
nervous system single? V^hat are the hemisphei'es of the brain ? 



THE NERVOUS SYSTEM. 



i^ 



Fie. 36. 




100 



FIRST BOOK IN PHYSIOLOGIC. 



14. In Fig. 37, you see the general arrangement oi 
the brain. It is a view of one of the halves or hem 
ispheres of the brain. It is the inside of the hemis- 
phere that you see. At ai and c is the cerebrum ; 
at/ is represented the white substance that joins thi8 
hemisphere to the other; at d is the cerebellum, 




9 



snowing a very beautiful arrangement, called the 
arhor vitce, or tree of life ; at e is the beginning of the 
spinal marrow ; at ff is the beginning of the nerve of 
eight, and at I is the nerve of smell. Then there are 
various other nerves, which go to the eye and other 
Darts of the face. 



37. 



Describe the representation of the brain and its serves, given in Fig 



THE NERVOUS SYSTEM. 



101 



15. You observe that the surface of the brain is 
very irregular. The brain does not touch the inside 
of the skull, but it is covered by three different mem- 
branes, one of which is very strong and thick, so as to 
protect this delicate organ from injury. 



Fio. 38. 




16. llie brain is soft, something like blancmange. 
It is the softest cfrgan in the body. It is composed of 
two kinds of substance. These are quite w^ell repre- 
sented in Fig. 38. Here the upper half of the brain 
is cut oft*, and you see the upper cut surface of the 

What is said of the surface of the brain, an^ of its coverings? What 
IS the consistence of tlie brain ? 



'02 FIRST BOOK IN PHYSIOLOGY. 

lower half. Tlie outer shaded part is a grayish sub- 
stance. All on the inside of this is a white substance. 
You see the dividing line between the two halves or 
hemispheres. In the middle of the Figure is repre- 
sented a substance which makes a connection between 
the hemispheres. It is probably by means of this 
connection that the two halves of the brain act toge- 
ther as one brain. 

17. It is curious to observe that the white part of 
the brain is just like the nerves. It is, like them, 
composed of very fine tubes. It is indeed a great 
central collection of the beginnings of nerves that 
branch out all over the body. 

18. The outer graj })art of the brain is, on the other 
hand, made up of cells, instead of tubes. This is sup- 
posed to be the working part of the brain. The mind 
acts directly upon the gray part when it moves any 
of the body. Thus, when you will to have your hand 
move, the mind does something, but what we know 
not, to some part of this gray substance. Then an 
impression or message is sent through those tubes in 
the white substance which are connected with this 
part of the gray substance. And as these tubes ex- 
tend from the brain in the nerves to the" muscles of the 
hand, the hand is moved. 

19. In sensation all this is reversed. The impression 
travels just the contrary way. It goes to the brain, 
and not from it, as it does in motion. If any one 
touches you, the impression is carried by the nervous 

What are the two kinds of substance in tlie braiu, and bow are tbey 
%rraDo;ed? What is tlie white substance? Of what is the gray sub- 
itance composed? W^hat is supposed in regard to it? What happens 
« mo' ion, aud what in sensation? 



THE NERVOUS SYSTEM. 10^1 



tubes to some portion of the brain. The gray sub- 
stance at this ])art of the brain receives the impression 
from the tubes in the white substance, and so the 
mind feels it. 

20. You observe that I have used the words impres- 
sion and message in speaking of the communication 
of the mind, by the nerves, with all parts of the body 
I use them because they are the best words that I can 
use in our present state of knowledge on this subject. 
We do not know what it is that is sent along the 
nerves. We only know that something passes, through 
these tubes whenever the mind feels anything, or ex- 
cites the muscles to action. And not knowing what 
it is, we speak of it as a message or an impression. 

21. There have been many suppositions on this sub- 
ject. Some have supposed that electricity travels 
along the nerves just as it does along the wires of a 
telegraph. They suppose that it goes from the brain 
when the mind excites the muscles to action, and that 
it goes towards the T^rain when we feel any sensation. 
Others have supposed that there was a vibration or 
shaking of the substance in the tubes of the nerves 
from one end of them to. the other. But these are 
mere suppositions, and there is no proof that they are 
trne. Whatever it is that passes through the nerves, 
it must pass through each of the multitude of little 
tubes separately, for, as you remember, each tube has 
no communication with any of the other tubes with 
which it is bound up. 

22. Not only are there different nerves for sensa- 

Do we know what is sent along the nerves ? What lias teen Rup 
:sed in reo^ard to it ? 



i04 FIRST BOOK IN PHYSIOLOGY. 

tion and for motion, as you learned in §10 and §11, 
but there are also difterent nerves for different kinda 
of sensation. Thus, the nerve that informs the mind 
of a tickling or a pain in the nose, is not the same 
nerve that informs the mind of the odors that you 
smell. The snuff-taker feels the tingling of the snufl 
with one nerve, and smells it with another. So, too, 
in the eye, the nerve with which the mind feels a 
pain there is not the same nerve with which it sees. 

23. There are also about the face different nerves 
for different kinds of motions. Thus, the nerve 
through which the lower jaw is moved, in eating, is 
not the same nerve by which the mind works the 
muscles of the jaw in laughing and in speaking. 

24. There is no organ that has so many difterenf: 
nerves as the eye. It has two different nerves for 
sensation and four for its various motions. Its ma- 
chinery of nerves and muscles is therefore very com- 
plicated. 

25. All parts of the body are not equally supplied 
with nerves. Some parts are very scantily supplied, 
and therefore have but little feeling, as it is expressed. 
There are few nerves in the bones, and so when a 
limb is cut off, the sawing of the bone occasions no- 
pain. There is not much feeling in the muscles, for 
although they are well supplied with nerves, the tubes 
in these nerves are the tubes for motion mostly, and 
few of them are for sensation. The skin has a full 



What is said in §22 of the different kinds of nerves ? What is sair 
of the nerves of motion in the face ? What organ has more nerves than 
any other i What is said of different parts of the body in regard t<i 
their supply of nerves ? 



THE NERVOUS SYSTEM. 105 

supply of the nerves of sensation. In cutting ofl' a 
limb, therefore, the cliief suffering is in dividing the 
skin. 

26 The skin is fully supplied with nerves for two 
purposes : 1, that it may act as the oi'gan of tphe sense 
of touch, and 2, that it may warn of danger. It is, 
as I have said in another place, a sentinel to guard 
the organs inside against injury. It feels the least 
touch. Its nerves at once send their w^arning of dan- 
ger to the mind, and the mind sends its orders for 
action to the muscles, so that the danger may be re- 
treated from. And as the skin stands guard so faith- 
fully, there is no need that the muscles and bones and 
other internal parts should be very sensitive. 

27. There is one office of the nerves that I have not 
mentioned. The different organs of the body sympa- 
thize with each other, and it is through the nerves 
that they do this. Thus, when you have a headache 
from a disordered stomach, it is because the brain 
sympathizes with the stomach. When tears flow in 
grief, it is because the tear-glands are excited to un- 
usual action through the nerves. The sympathy in 
^his case is with the brain. The sorrowful mind, by 
its thoughts, affects the brain. Then the tear-glands, 
by means of the nerves which go from the brain to 
them, sympathize with it, and so they make and pour 
forth a flood of tears. 

28. There are many actions in the body that result 
from the connection of different parts by the nerves. 

For what two purposes is the skin fully supplied with nerves ? Why 
is there no need that tlie muscles and bones should be very sensitive? 
B^ what is the sympathy of the different organs of the body maintained ' 



106 FIRST BOOK IN PHYSIOLOGY. 



Thus, when there is something in some of the pipes 
of the lungs, causing an i7Titation there, we cough in 
order to throw it off through the windpipe. But the 
muscles that perform the coughing motion are not in 
the pipes. They are outside of the lungs in the frame- 
work of the chest, and remove the irritating substance 
by forcing the air out against it. Now the reason 
that these muscles are excited to this action is that 
they are connected by nerves with the pipes where 
the irritation is felt. So it is in sneezing. If some- 
thing irritate the lining membrane of the nose, the 
muscles of the chest throw the air from the luno^s with 
great force up through the nose to expel the offending 
substance. They could not act in this way if they 
were not connected by nerves with the lining mem- 
brane of the nostrils. A message, as we may say, is 
sent from the irritated spot down to the muscles of 
the chest through the nerves, telling tliem to send up 
a blast of air to expel the intruder. 

29. From what I have told you in this chapter m 
regard to the nerves, you can see that the nervous 
system is a very complicated system. I have spoken 
only of those things in it which you can easily under- 
stand. In my larger work on Physiology I go into 
this subject much more extensively, and what you 
have learned in this book will prepare you to under- 
stand fully what is contained in that. 

Upon what do many actions in the body depend ? Ulustrale by tlw 
&"*:€ of coughing and sneezing. 



THE BONES. 107 



CHAPTER VIII. 
THE BONES. 

1. The bones of the body serve many different piu^ 
poses. The three principal of these I will notice. 1. 
They form the solid framework of the body. In this 
respect they are to the body what timbers are to a 
building. 2. Some of the principal bones also form 
cavities in which important organs are securely in- 
closed. Thus, the soft delicate brain is made very 
secure by being inclosed in that round box of bones 
called the skull or cranium. So, also, the lungs and 
the heart, as you saw in the chapter on Respiration, 
are very carefully shut up in a barrel-shaped frame 
of bones, united firmly by ligaments and muscles. 3. 
The bones serve another important purpose in being 
moved by muscles. When they move upon eacli 
other at the joints it is the muscles that make them 
move. The bones are, therefore, a part of the ma- 
chinery that the mind moves by means of the ner- 
vous system. This use of the bones shows you why I 
introduce this subject here. 

I have told you in Chapter II, §3, of what two 
substances the bones are composed, and shall, there 
fore, say nothing here on that subject. 

2. The bones in our bodies are covered up from 
view by the ligaments, muscles, tendons, and the skin. 
But this is not so with the skeletons of all animals. 
Some have their skeletons on the outside of the body. 

What are the three principal purposCvS that the bones answer ? Of 
<vhat two kinds of substance are the bones composed? 



108 FIRST BOOK IN PHYSIOLOGY. 

This is the case, for example, with turtles, crabs and 
lobsters. With them the skeleton is a coat of mail to 
defend the soft parts from injury. 

3. The bones, although they are so hard, grow 
together with all the soft parts that surround, them. 
Thus, when the arm of a child grows to be the stout 
arm of a man, the bones enlarge equally with the 
muscles, tendons, &c. They enlarge, just as these 
other parts do, from particles added by the formative 
vessels from the blood ; for, although they are so 
hard, the blood circulates in them. 

4. The teeth, which are so much like the bones, 
differ from them in regard to growth. When a tooth 
first shoots up out of the gum, its body is as large as 
it ever will be. It cannot grow larger, as the bones 
do, because the hard enamel can have no circulation 
in it. If the teeth could grow larger there would be 
no need of having a second set to take the place of 
the iirst. There would then need to be simply an 
addition of more teeth as the jaw enlarged. But as 
it is now, all the first set are removed, because they 
would be too small for the large jaw of the adult, and 
thirty-two large teeth take the place of the twentv 
small ones of the first set. 

5. The bones are not perfectly solid. They would 
be too heavy if they were so. Some parts of them 
are made up of cells, as the large ends of the long 
bones. The shafts of these bones are hollow. This 
is for the purpose of making them strong, and at 

By what are the bones in our bodies covered ? Are they covered up 
in all animals? What is said of the growth of bones? How do teeth 
•liiier from bones? Vv'hy are there two sets of teeth ? 



THE BONES 



10^ 



Fig. 3!» 



tiie same time light. In Fig. 
39 you see the thigh-bone and 
the bone of the arm. In both 
the shaft is hollow, while tlie large 
ends are chiefly made up of cells. 
In birds it is very necessary that 
the bones should be light while 
they are strong, so that they may 
not be burdensome in flying. In 
them, therefore, the bones are 
very hollow. They are so for the 
same reason that the stalks of tall 
grass and of grain are* hollow. If 
these were solid, and therefore 
more slender, they would break 
very easily as the wind bent tliem 
over. And in constructing build- 
ings, the architect very well 
knows that a hollow pillar has 
more strength than the same 
quantity of wood in a solid form. 

6. The bones have a great variety of shapes accorvl 
ing to their diflerent uses. You see this to be true as 
you look at the skeleton in Fig. 40. In the skull, 
which holds the brain, you see the bones so shaped 
and arranged as to form a somewhat round box. At 
the under part of this box in front are bones of various 




shapes to accommodate the 



of four of the 



Why are the bones not solid ? How are t"he long bones at their ends! 
Why are the sliafts of tliese bones hollow ? Why are they very holloa 
1 birds ? What i' said of the stalks of pl^^nts and the pillars of build 
t.irs ? 



*10 FIRST BOOK IN PHYSIOLOGY, 



Fio. 40. 




i'HE BONES. 



ii: 



Beaiifcs, c^be'ug, hearing, tasting and smelling. Then 
there i6 ^Jie bone of the lower jaw, shaped something 
like a hoisoshoe. The bones of the chest form a bar- 
rel-shaped cavity for the heart and lungs. The spinal 
"iolumn^ ^, made up of twenty-four bones, extends the 
whole length of the body as its main pillar. To this 
are fastened the slender ribs which are joined to the 
flat breast-bone il^ front by means of cartilages. The 
spinal column, you observe, stands firmly supported 
upon a thick bone which is wedged in between two 
broad flaring bones, I and m. This bowl-form collec- 
tion of bones, called the pelvis, supports the contents 
of the abdomen. You observe the large bones of the 
thigh and leg, w^hich are made for firmness, and the 
lighter bones of the upper extremity, w^hich are fitted 
for quickness and variety of motion. I w^ill now no- 
tice some of the bones more particularly. 

7. In Fig. 41 you see the bones of the head — that 
is, all of them thg,t are in 
sight in front. There are 
twenty -two bones in the head, 
but some of them are out of 
sight. Fourteen of these be- 
long to the face. Eight be- 
long to the cranium, that is, 
the part of the skull that 
holds the brain. Of these 
observe particularly the large 
bone of the forehead, a, 
called the frontal bone, the 



Fig. 41. 




What is said of the shapes of boues ? Describe the skeleton &s rep- 
resented in Fig. 40. How many bones are there in the head? Ho-w 
many of them belong to the cranium ? Describe thfse as seen in Fii,'. 41 



12 FlKiST BOOK IN PHYSIOLOGY. 

paTietal bone, h^ and the temporal bone, or bone of the 
temples, c. There is a bone in the rear, forming the 
back of the cranium, as the frontal bone forms the 
front. These bones, with two others on the under 
part of the cranium, make the round box that holds 
the brain. 

8. The cranium is made round because it will not 
break as easily as it would if it were of some other 
shape. This is one reason also why it is made up of 
so many different bones, instead of being one solid, 
tiglit box. If a blow be received on the head, these 
bones give a little upon each other, as it is expressed, 
and so they are not often broken. They give more 
in the child than in the adult, because, besides being 
less brittle, they are less tightly put together. It is 
well that it is so ; for if it were not, the skull would 
often be fractured, in the frequent falls which the 
child has. 

9. The bones on the top of the head are fastened 
together by what are o.^^^ sutures. They are locked 
together by little teeth of bone, w^hich shoot by eacL 
other, as you see in Fig. 42. Here h is the suture 
across the top of the head between the two parietal 
bones : (2(2 is that between the two parietal bones and 
the frontal bone in front ; and c g\'^ that between the 
parietal bones and the bone at the back part of the 
cranium. In the young child these joinings by 
suture are not formed, and in the infant the bones are 
quite apart in some places, especially at the upper part 
of the forehead, as you can perceive by the touch. 

"Why is the cranium rounci ? Why is it made of so many bones ? 
What are the sutures of the skull ? What is said of the joinings of the 
bones of tlie skull in the child ? 



THE BONES. 



113 



Fig. 42. 




10. The l)ones of the cranium, together with their 
cioverings, are well fitted to guard the delicate brain 
from injury by the blows to which the head is so 
much exposed. When a blow is received, its force is 
broken by the hair, the skin, and the muscles, that 
extend over the bones. And then the bones them- 
selves, as I have before said, give a little upon each 
other. It requires therefore a very hard blow to 
break the skull. 

11. The spmal column is the most wonderful part 
of the bony machinery of the body, because it serves 
80 many diflferent purposes. It is the great pillar of 
the body, and yet it is a chain of twenty-four bones, 
that can be, bent considerably, especially in some 
parts of it. And besides, there is a canal moving 
through all this chain of bones, in which lies securely 
the spinal marrow, an organ as delicate and as essen- 

Hcw is the delicate brain guarclel against injury? Mention tbe sev 
*jral uses of tLe spinal ccIudtm ? Of how many vertebr«Te is it coniposed ♦ 



tl4 



FIRST BOOK IN PHYSIOLOGY. 



tial to life as the brain itself. Then there are nerves 
branching out from the spinal marrow, between the 
twenty-four bones, in such a way that they are neve^ 
pressed upon. 

Fig. 43. 
C 



Fis.44. 




12. The twenty-four bones of the spinal column are 
called vertelrce^ (plural of vertebra.) In Fig. 43, you 
see one of these vertebrge ; a being the body of the bone; 
h the hole through the vertebra which forms its part 
of the canal for the spinal marrow*; and c the spinous 
'process^ as it is called. The hard ridge that you feel 
in passing your finger up and down the middle of the 
back, is the row of these spinous processes. Each ver- 
tebra has six other processes, only two of which you 
can Boe in the figure. The bones of the whole column 
are so locked together by these processes, that they 
cannot be separated from each other or dislocated 
without being broken. In Fig. 44 you have a side 
view of the same vertebra. As you look at the spinal 

Descrilie the vertebrae as represented in Figs. 43 and 44. How many 
processes or projections has each vertebra ? What is the use of thera' 
By What are they covered ? 



THE BONES. 



115 



Fig. 4.1. 



coluran in front, it in a round smooth column ; but in 
the rear the processes make it verj jagged. These 
are all, however, ^jovered up by muscles, except the 
roM^ of spinous piocesses. 

13. In Fig. 45, you see the whole col- 
umn, with tbo stout bone on which it 
stands. It is represented as sawn down 
through its whole length, so that you see 
but half of it. You see the bodies of the 
vertebrae in front, and the spinous pro- 
cesses on the other side. Between the row 
of the bodies of the vertebrae and the row 
of spinous processes you see the canal in 
which lies the spinal marrow. You ob- 
serve that there are spaces between the 
bodies of the vertebrae. These spaces 
aie filled with pieces of cartilage or 
gristle. If it were not for these carti- 
lages you could not bend the back-bone 
forward at all, but cOuld onlj" bend your 
body on the heads of the thigh-bones, 
with a hinge-like motion, which would 
be very stiff and awkward. As it is, 
when you bend forward, in addition to 
this hinge-like motion, the bodies of allj 
the vertebrae come nearer together. Ini 
doing so the cartilages between them are 
compressed, and so are made smaller. 
And as you straighten up again, these 
cartilages, by their elasticity, return to their usual 



Describe the spinal column as represented in Fig. 45. Of what use 
V fi the cartilages ? 



116 FIRST BOOK IN PHYSIOLOGY. 

size again. From the constant pressure on these car 
tilages, as you go about during the day, you are noi 
quite as tall at night as you are in the morning. So 
also in old age, one becomes less tall than in the vigo>" 
of manhood, because these cartilages shrink. 

14. The spinal column can be bent not only for- 
wards, but in other directions also — to either side and 
backwards. This chain of bones can also be some- 
what twisted, as we may express it, as you turn your 
body one way and another. As yon do this, each 
bone moves with a rotary motion a very little. But 
as there are twenty-four bones, all these little motions 
between them together make a considerable twist of 
the whole column. Now, as there is through the 
whole length of this column a rod of very delicate 
substance that must not be pressed upon, all these 
motions have to be most carefully arranged. The 
bones must be nicely fitted with all their processes ; 
they must be well fastened together with ligaments; 
•and then the muscles that move all these twenty-four 
bones must all of them work exactly aright. All this 
is done, and the back-bone, as we call it, is a set of 
machinery vastly more complicated and more nicely 
arranged than any machinery that man ever con- 
trived. 

15. But the most wonderful part of this machinery 
is at the top of the column. There the motions are 
more free than in any other part of the column, as 
yon see when you bow your head, and bend and turn 

In what part of the day are you the tallest ? What is said of thfl 
various motions of the spiue ? What is said of it as a piece of machine 
ry ? What is the most wonderful part of this machiuerv ? 



THE BONES U*? 



it in various directions. There are two different mo- 
tions made by the head on the top of the column. 
The first of these is when yon move the head back 
ward and forward. In doing this it rocks on the firsi 
vertebra, the topmost bone of the spinal column. 
For this purpose there are tw^o smooth rounded sur 
faces, that work in two smooth, hollow places in the 
vertebra. 

16. The other motion is when you turn your head 
to look at the one side or the other. In performing 
this rotary motion the skull does not move alone, as 
in the first motion, but it moves together with the 
first vertebra. The first vertebra in this motion 
moves on the second around a tooth-like process that 
stands up from this second vertebra. This tooth 
works in a smooth notch on the inside of the first ver- 
tebra. It is bound very fast in this notch by a strong 
ligament, so that it may not, in any of the quick mo- 
tions of the head, be made to press fig. 46. 

on the delicate spinal' marrow which 
lies against it. In Fig. 46 you see 
these two vertebrae, and notice the 
tooth-like process of the second 
standing up on the inside of the 
first vertebra. 

17. You see, then, that when you move your head 
backward and forward, you move it in a hinge-like 
way on the first bone ^f the spine ; and when you 
turn the head to look to the right or the left, you 

How many motions are performed by the head on the top of the 
spinal column ? Describe the manner in which the first of these motions 
18 performed. Then the second. 




118 FIRST BOOK IN PHYSIOLOGY. 

turn the head and this first bone together as one 
thing on the tooth-like process of the second bone. 
There is an arrangement somewhat like this in the 
standard of telescopes. There is first a hinge-joint^ 
as in the case of the head, so that you can move the 
telescope up and down so as to look as high or as low 
ds you wish. There is, also, in the standard anothei 
joint, with a rota/ry motion, by which you can turn 
the telescope so as to see as far to the one side or to 
the other as you please. This is like the motion per- 
formed between the first and second vertebra. 

18. The vertebrae vary much in difi^erent kinds of 
animals. Here, for example, in Fig. 47, is the verte- 
bra of a fish, which you see difi'ers very much from 
the vertebrae of man, as represented in Figs. 43 and 
44. It has but two processes,/*/*. In man there is a 
Firx.47. single short spinous process behind, while 
the vertebra is round in front. But in the 
fish there are two quite long spinous pro 
cesses, one in fron^ and the other in the 
rear ; or rather, we should say, according 
to the common position of the fish in the 
water, one above and the other below. 
There is a curious contrivance in the ar- 
rangement of the vertebrae of the fish for 
making the spine flexible. Each vertebra has a cup- 
like cavity on each side towards the next vertebra. 
Each two vertebrae then put together make a cavity 
of this /N shape. This cavity is lined with a 

Give the comparison between this arrangement and that of a stand 
ard of a telescope. Describe the vertebrsB of a fish and their arrange 
ment. 




THE BONES. ^^ 



membrane making a sac, and in this is a fluid some- 
thing like the white of an egg. These sacs, thus 
filled with fluid, make soft cushions between all the 
bones of the spine, upon which the bones rock in the 
various motions of the fish. This arrangement you 
can observe for yourself whenever you have fish on 
the table. 

19. In snakes the spinal column is exceedingly 
flexible. It is made so in two ways. First, there is 
a o-reat number of vertebrae. The result of this is, 
that in a very extensive motion of the whole spine 
the motion between each two vertebrae is very little. 
The motion is divided up, as we say. The rattlesnake 
has over two hundred vertebrae, and the great noa- 
constrictor has three hundred and four. Secondly, 
the flexibility of the spine of these animals is secured 
by having a ball and socket joint between all the ver- 
tebrae. A smooth round ball in each vertebra w^orks 
in an equally smooth cup-like hole in the one next to it. 

20. The framework of the chest I have described to 
you in the chapter on Respiration § 10. There are 
two bones outside of this barrel-shaped framework 
that I will now notice. First, there is the collar-bone 
y, Fig. 40. This is fastened to the breast-bone at one 
end, and at the other end is fastened to a process of 
the shoulder-blade, and helps to make the top of the 
shoulder. It is a sort of prop or brace, that keeps the 
shoulder braced out in its place. 



By what two means are the spinal columns of snakes made soflexi 
Die? How many vertebrae has the rattle-snake? How many has the 
boa-constrictor ? What is the use of th(; collar-bne, and how is it 
placed ? 



120 FIKST BOOK IN PHYSIOLOGY. 

21. The shoulder-blade is a very singular bone. Its 
back part, that which is towards the spine, is quite 
thin, and is covered on both sides with muscles that 
move it. It is designed to give freedom to the mo- 
tions of the arm. AVhen • you draw your arm back 
very much, you can see that there is considerable mo- 
tion of the shoulder-blade. This is because the mus- 
cles that are attached to it pull it back, at the same 
time that other muscles pull the arm in the same 
direction. And as the shoulder-blade forms at its 
upper part the shoulder-joint, these muscles in pulling 
back the bone pull back the whole joint, and of course 
the arm with it. Ton can see that the arm could not 
be drawn so far back if the shoulder-joint were made 
without any shoulder-blade. It could have been so 
made, but it would have been awkward and stifi* in 
its motions. 

?;2. Where the shoulder-blade forms the shoulder- 
joint there is a shallow cup-like surface, lined with 
cartilage, which is as smooth as the finest polished 
ivory. The bone of the arm which fits into it has its 
end in the form of a ball, which is also tipped with 
cartilage as smootli as that in the cup. Observe what 
keeps this ball in the cup as it moves about in it. 
There is a thick skin attached all around the edge of 
the cup and fastened down over the ball. Besides 
this stout ligament, there is another remarkable con- 
trivance for keeping the round head of the bone in its 
place. The tendon of a large muscle works in a 

Describe the arraogemeut of the shoulder-blade. How does it make 
the motioDs of the arm free ? Describe the shoulder-joint. Jn wba-t two 
wa^- s is the joint guarded against dislocation? 



THE BONES. 121 



groove on the front of this head of the bone, and thus 
holds it so as to keep it from slipping out of the cup. 

2»3. It is necessary that the joint should be thus 
carefully guarded, because the cup or socket is so 
shallow. As it is, although it is so well guarded, it is 
very often dislocated. It might have been made 
more secure by having the socket deeper ; but then 
the motions of the arm could not be as free as they 
are now, and freedom of motion you can readily see 
is very important in this part of the machinery of the 
body. 

24. The arm-bone, % Fig. 40, is jointed at the 
elbow, with the two bones of the fore-arm (so called) 
and seen at o and n. The elbow-joint is different alto- 
gether from the joint at the shoulder, for the motion 
is in one direction only, back and forth like a }iinge. 
It is therefore called a hinge-joint, while that at the 
shoulder is called a ball-and-socket-joint. In whirling 
a skipping-rope, you use the joint at the shoulder; but 
in striking with a hammer, you use the hinge-joint at 
the elbow. 

25. The hand moves on the fore-arm at the wrist 
with a hinge-joint. The fingers have hinge-joints, 
except where they are joined to the hand. There 
they have, besides the hinge-like motion, something 
of the motion of a ball-and-socket-joint. The motions 
of the thumb are, as you see, quite different in some 
respects from those of the fingers. 



Why is this joint so carefully guarded ? How cowld it have beec 

made more seeriie? Why was it not? Describe the elbow-joint 

How does it difi'er from the shoulder-joint? Describe the joints of th* 
vrist and fmgers and thumb. 



122 FIRST BOOK IN PHYSIOLOGY 



^**- ^' 26. Besides these mo 

tions that I have descri- 
bed, there is a rotm'^ 
motion of the arm, as 
you turn the palm of 
the hand up and down. 
This is done by a pecu- 
liar motion of the two 
bones of the fore-arm. 
I will make this clear to 
you by Fig. 48. You 
see that the largest end 
of the ulna^ a^ is at the 
elbow, while the largest 
end of the radius^ 5, is 
at the wrist. Now, the 
hinge-like motion at the 
wrist is performed whol- 
ly with the large end of 
the radius. The small 
end of the ulna, marked 
(?, has nothing to do with 
it, but is loose, and has a rolling motion on the end of 
the radius. It is just the reverse with these two bones 
at the elbow-joint. The hinge-motion there is per- 
formed with the large end of the ulna, a^ and the small 
end of the radius, J has nothing to do with it, but rolls 
on the end of the ulna. 

27. The effect of this arrangement is this. When 
the palm of the hand is upward, as represented in the 




How is the rotary motion of the fore-arm made^ 



THE BONES. 12:i 

Figure, these two bones are, as you see, nearly paral- 
lel. But when the palm is turned over, they are, a^i 
we may say, twisted upon each other, the ulna, (Z, roll- 
ing on J, at its lower end, and the radius, 5, rolling on 
a, at its upper end. You can see these two positiontj 
of these bones in Fig. 40. In the right arm you see 
the palm of the hand towards you, and the radius and 
ulna are parallel. In the left arm the palm is partly 
turned from you, and these bones are twisted upon 
each other by their rolling or rotary motion. 

28. Observe now how many different motions there 
are in the arm and hand. They are, the motion of the 
ball-and-socket-joint at the shoulder, the hinge-motion 
at the elbow, the rolling of the two bones at the fore- 
arm upon each other, the hinge-motion at the wrist, 
the hinge-motions of the fingers at their joinings with 
the hand, together with something of a ball-and-socket- 
motion, the hinge-motions of the other joints of the 
fingers, and the free .motions of the thumb differing 
somewhat from those of the fingers. 

29. In observing these motions you will see the rea- 
son why there are different kinds of motion in differ- 
ent parts of this complicated machinery. You can 
see, for example, why there is a hinge-motion in one 
place and that of a ball-and-socket joint in another, 
and why the two motions are united in the joints 
which the fingers make with the hand, while the 
other joints of the fingers can perform only the hinge- 
motion. 



Mention the different motions of the arm and hand in their order, be 
ginning at the shoulder-joint. What is said of the two kinds of motior 
the hmsre-like and the ball-and-so«>ket-motion ? 



124 



FIRST BOOK IN PHYSIOLOGY. 



^^«' ^^- 30. You see that there are 

many bones in the hand — 
twenty-seven in all. There 
are eight small bones called 
the carpal bones, represented 
at d^ in Fig. 48. These are 
tightly packed together, and 
lie next to the bones of the 
fore-arm. The metaearjpal 
bones, e^ make the frame- 
work of the flat part of the 
hand. They are very much 
like the first row of the bones 
of the fingers,/*. But they 
are firmly bound together by 
ligaments. These ligaments 
you can see in Fig. 49. At 
dd^ you see those that bind 
the metacarpal bones together at their beginning, and at 
e e^ those that bind them at their ends, where the bones 
of the fingers are jointed with them. At a^ J, c^ and g^ 
are other ligaments that bind the carpal bones together. 
31. You notice that there are twelve bones in the 
frame-work of the hand, aside from the fingers — that is, 
the eight carpal and the four metacarpal bones. The 
chief reason for having so many bones thus packed 
together is this. Although they are bound together, 
there is some little motion between them, and this 
makes the hand more light and springy than it would 
be if these twelve bones were all in one. 

How many booes are there in the hand ? Describe their arrangement 
How many bones are there in the framework of the hand ? Why ar« 
there so many ? 




THE BONES. 



125 



32. The bones of the lower extremities have not so 
much freedom of motion as those of the upper. The 
chief object is firmness, as they support the weight of 
the body in moving about. They are larger there- 
fore than tlie bones of the upper extremity, as you see 
in Fig. 40, and their joints are much more stout and 
."secure. 

33. In Fig. 50, you have a rear 
view of the thio-h-bone. Its round 
head, a, fits into a deep socket in 
the pelvis, as represented in Fig. 
4:0. Observe the reason of the dif- 
ference in regard to the depth of 
the socket between this joint and 
the shoulder-joint. In the hip-joint 
strength is especially needed ; while 
freedom of motion is more needed 
in the joint of the shoulder, and so 
its cup or socket is made shallow. 
The head of the thigh-bone is held 
in its socket by the same kind of 
ligament that I have described in 
§ 22, as securing the shoulder-joint. 
It clasps the neck of the bone, c^ 
and is fastened all around the edge 
of the socket. There is another 
ligament also. At h you see a little 
liole, in which one end of this liga- 
ment, which is short and stout, is 
fastened. The other end is attached 

What is said of the difference between the bones of the upper and 
the lower exti-emities ? Describe the thidvbone. Why is the socket 
of the hip-joint deeper than that of tlie shoulder-joint? Describe th^ 
'iiraraeDtB of the hip joint. 




126 FIRST BOOK IN PHYSIOLOGY 



to the bottom of the socket. At d and e are two pro- 
jections, to which are attached large muscles, that 
move the thigh. Along the whole length of the bone 
is a rough ridge. A, for the attachment of muscles. At 
^ and k are two smooth surfaces, which form with the 
large bone of the leg, the hinge-joint at the knee. 

34. There is a small thick bone fitting over the 
knee-joint in front, called the knee-pan. This is seen 
at t^ in Fig. 40. One of its uses is to shield the joint. 
It wards oflf blows, and prevents the joint from being 
injured bj^ falls. It has another verj important use, 
of which ! speak particularly in my larger work on 
Physiology. 

35. The leg has two bones. One of them, u^ Fig. 
40, is very large. It sustains the whole weight of the 
body. It has two smooth surfaces at the knee-joint, 
on which w^ork the two smooth surfaces of the thigh- 
bone, i and ^, seen in Fig. 50. The other bone of the 
leg, t;. Fig. 40, is very slender. It is firmly connected 
with the large bone by ligaments and muscles. The 
two chief uses of this bone are, to furnish a hold for 
some of the muscles, and to make the outer side of 
the ankle-joint. The inner side of this joint is made 
by the larger bone. This joint is made by these tw^o 
bones projecting down over a bone in the foot repre- 
lented at /, in Fig. 51. It is a hinge-joint. It is 
made quite loose, however, so that the foot can be 
turned inward and outward. And yet it is a very 
firm joint, for the bones of the leg jut over strongly 
on each side, and the ligaments are very stout. 

What is said of the knee-pan ? Describe the bones of tlie leg. What 
are tbo uses of the small boue of the leg ? What is said of the anklp* 
joint ? 



THE BONES. 



127 



36. In Fig. 51 are represented the bones of the foot. 
At e dfg and h are the seven bones of the tarsus ; at 
a are the five bones of the meta-tarsus / and at h and 
c are the fourteen bones of the toes — twenty-six in all. 



Fio. 51. 




The reason for having so many bones in the foot is 
the same as that stated in regard to the hand in §31. 
The springiness thus given to the foot is quite im- 
portant in guarding against shocks. You can realize 
this if in jumping you come down on your heels, in- 
stead of coming down on your feet as is usually done. 
Some animals that leap much have special guards 
against shocks in the thick elastic cushions on the bot- 
toms of their feet. Tou can see these in the cat and 
dog. 

37. The arched form of the foot assists in giving 
springiness to it. You can see that the tread is much 
less elastic when the foot happens to be flat. This 

How many bones are there in the foot ? Why are there so naany f 
What is said of the importance of elasticity in the foot ? What contriv 
ances are there in the feet of some animals ? 




128 FIRST BOOK IN PHYSIOLOGY. 

arched form is represented in Fig, 52, which gives a 
side view of the bones of the foot. In this figure the 
Fig. 52. boncs of the tarsns ex- 

tend from the heel to a ; 
the meta-tarsal bones 
are at h ; and the bones 
of the toes are at c. In 
every movement of the 
foot there is some little 
motion between all these bones, and it is this that 
gives ease and grace to its motions. Observe what 
is the order of its movement in walking. The heel 
first touches the ground, as represented in the figure. 
Then, as tne body moves forward, the ball of the 
foot at h presses firmly on the ground as the heel 
rises. Now, as the change of pressure is made from 
the heel to the ball of the foot, there is a little giving 
between all the bones of the tarsus a and the meta- 
tarsus J, and this makes the motion an easy one. If 
all this part of the foot were one bone, the motion 
would be stiff and awkward, and not elastic and 
graceful as it now is. 

38. The ends of all the bones are tipped with carti- 
lage so that they can move easily upon each other. 
And besides this, the ends thus tipped with this fine 
but smooth substance are lined with a very fine mem- 
brane, so arranged as to make a close sac. This you 
can understand by Fig. 53, in which a and h are the 
ends of two bones, the sac c being represen',ed as se- 

What is said of the arched form of the foot? Describe tfc« movement 
^f the foot in walking. How is it made easy and graceful '* With whaJ 
are the en(]s of the V)oiie. tipped ? 



THE BONES. 1^9 




Fio. 53. parated from the bones, in order that 

the arrangement may be clear to you. 
It is as if a little bladder were placed 
between the bones, fastened on all 
over the two surfaces at their ends. 
This bladder or sac has a little fluid in 
it like the white of an egg. This fluid 
is to our joints what oil is to the joints 
of machinery. When a train of cars 
stops at a station you see men with 
their little cans oil the boxes of the 
wheels both of the locomotive and the 
cars. And great pains is taken wdth the joints of 
all kinds of machinery to keep them oiled. Bui 
the joints in our bodies keep themselves oiled, as we 
may say. It is done in this w^ay : The fluid in the 
sac of a joint oozes from the inner surface of the sac, 
just as the perspiration comes from the pores of the 
skin. But the same fluid does not remain in the 
joints year after year. Such constant rubbing would, 
after a while, make it unfit for use. It is, therefore, 
constantly renewed. There are all over the inside oJ 
the sac little absorbing vessels that take up the fluid 
as fast as it becomes unfit for use, and there are secre- 
ting vessels that pour out fresh fluid to take its place. 

What other provision is there for the easy working- of the joints ? 
Compare with common machinery. How is the fluid in the saco of tht 
joints kept fresh ? 

6* 



i30 FIRST BOOK IN PHYSIOLOGY. 



CHAPTER IX. 

THE MUSCLES. 

1. I MAVK already explained to you in Chapter II. 
die manner in which the muscles act. You there saw 
that when a muscle acts, its fibres all shorten them- 
selves. Now, when a muscle contracts or shortens 
itself, it swells out or becomes thicker. You can see 
this if you watch the bare arm of some one who is at 
work. You can feel this swelling of the muscles in 
your own arm as you move it. Straighten out your 
arm, and then grasp it with your other hand half-way 
from the elbow to the shoulder. Now bend up your 
arm forcibly, and you will feel the large muscle on 
the front of your arm swell out and harden as you 
grasp it. It is just as it is with a piece of india-rub- 
ber. If you stretch out the india-rubber, it becomes 
smaller ; and then if you let it go, it contracts like the 
muscle, and as it contracts, it, like the muscle, becomes 
thick again. 

2. The muscle, however, contracts in this case frc^m 
a difierent cause than that which makes the india 
rubber contract. The india-rubber contracts because 
it is stretched — it merely goes back to its usual state 
by its elasticity, as it is termed. But the muscle has 
a power of contracting which is something more than 
elasticity. It contracts because the mind tells it to 
do so by means of the nerves, the telegraphic wires 

What is the state of a muscle wheu it contracts? Make the compar- 
isoD between the muscle and india-rubber. How do they differ, froir 
each other in the causes of their contraction ? 



THE MUSCLES. 131 



tliat go from the mind's seat, the brain. The nerves. 
as I have told 3^011 in the chapter on the Nervous Sys- 
tem, branch out and distribute their fibres to all the 
fibres of the muscles. And every fibre of a muscle 
thus receives a message from the brain whenever tlie 
muscle contracts. 

3. The muscles have elasticity, just as the india- 
rubber has. and there is a contraction in them by 
means of this elasticity. This is seen when a muscle 
is cut in two, by accident, or, as is sometimes done, in 
the operations of the surgeon. In this case the two cut 
ends separate from each other considerably, because 
they are drawn apart by the contraction of the fibres 
of the muscle. But this contraction does not take 
place from any message sent to these fibres from the 
mind. It arises from their elasticity simply, just as 
the contraction of the india-rubber arises from its 
elasticity. Muscles, then, have two kinds of contrac 
tion. The one kind is from their elasticity ; the othei 
is when they are excited to action through the nerves. 
I shall speak of these two kinds of contraction in an- 
other part of this chapter. 

4. Muscles commonh^ end in tendons. While the 
muscles are red, the tendons are white and shining. 
Tendons are the ropes or rigging with which the mus- 
cles pull the bones and other parts. They are of dif- 
ferent shapes. Some of them are long and slender. 
Voti can see tendons of this shape on the back of the 
liand very plainly in thin persons. The muscles that 
work them are in the full arm above. You can see 

Slr)W liow the muscles Lave two kinds of contraction What Q.re 
tt^ii(l<'ns ^ WliMt is snid of their shape ? 



132 FIRST BOOK IN PHYSIOLOGY, 

that this is so, if while you work your fingers back 
and forth, you take hold of the arm a little below the 
elbow with the other hand. You feel very distinctly 
there the movement of the muscles as they contract 
and relax themselves. 

5. The tendons are much smaller than the muscles 
that pull them. You can see this in the case of the 
hand and arm. The muscles that move the hand and 
the fingers make up the full part of the arm ; but the 
wrist, where their tendons go to the hand, is very slen- 
der, because these tendons are so small. You can see 
the same thing in the " drumstick" of a fowl. In the 
slender leg are the tendons lying along the bone, 
while the bulky muscles that work them are above. 

6. While the tendons are so small, they are very 
strong. It is exceedingly rare to have them break, 
even in the most violent efi*orts. It is well that it is 
so, for it is very difiicult to heal a broken tendon. 
When a bone is broken, the two ends can be held 
accurately together, and therefore are easily united. 
But when a tendon is broken the muscle to which it 
belongs draws the part that is fastened to it away 
from the other end. And, therefore, with the very 
best of care, it is difficult to make them heal at all. 

7. I will now speak particularly of some of the 
muscles, that you may understand how they act. In 
Fig. 54 is represented the lower part of the larg*e 
muscle that raises the heel when we walk. The large 
bone of the leg and the bones of the foot are repre- 
sented. P, the muscle, makes up most of the bulk oT 

What is said of the size of the tendons ? What of their otrength f 
Why is it difficult to heal a broken tendon ? 



THE MUSCLES. 



13:] 




the calf of the leg. 

The weight of the body 

rests upon the bone W. 

J^'ow, in walking, as 

we raise the body in 

taking a step, we do 

it first by raising the 

heel with the muscle 

r, the pressure being 

on the ball of the 

foot, F. This muscle does here with the weight of the 

body what the muscles of your arms do to the load in 
a wheelbarrow when you raise it by the handles. 

8. In Fig. 55 are represented two of the principal 
muscles of the arm, 4 and 7. Between these is the 
bone of the arm, 1, and at 2 are the bones of the fore- 
arm, as the part of the arm below the elbow is com- 
monly called.' At 4 is the muscle that acts when you 

Fig. 55 




bend the arm at the elbow. At 5 is its double attach- 
ment at the shoulder-joint, and at 6 is where its ten- 



Desoiibc the arrangement and action of the musclp represented in 
F'iy. 54 Describe the muscles lepi-esented in Fig. .5.5- 



lo4 FIRSl 15 00K IN PHYSIOLOGY. 



don is fastened to the radius, one of the bones of the 
fore-arm. 1 have described the manner in which this 
muscle acts in Chapter 11. § 10. The muscle that acts 
in opposition to this, and straightens the arm out, is 
at 7, and is fastened at 8 to the point of the elbow. 
When you bend and straighten your arm by turns, 
these two muscles take turns in acting, like two saw- 
yers that are working a long saw back and forth. 
While one sawyer pulls, the other lets the saw go. So 
it is with these muscles. When the muscle 4 contracts, 
the muscle 7 is relaxed ; and when 7 contracts, 4 is re- 
laxed. And so it is wdth other muscles. Thus, when 
you swing your leg back and fortli, there are two sets 
of muscles that perforin these two opposite motions, 
and while one set are contracting, the other are relax- 
ing. So it is with the motion of the low^er jaw up 
and down in eating. While the muscles that move 
it up are contracting, those that pull it down are re 
laxed; and then, while those that pull it down 
contract, those that draw it up are relaxed. 

9. In Fig. 56 you see represented some of the mus- 
cles of the face and the neck. At h is a large, spread- 
ing, fan-shaped muscle, which, with another muscle, 
c, raises the lower jaw, in eating. You can perceive 
the action of this muscle, if you place your fingers 
on the temple of either side, while you move the 
jaw up and down. This is quite a large and pow 
erful muscle. Observe, how well it is packed over 
the side of the head, so as to make no uncomely 

Give the comparison made in regard to their action. What other 
illustrations are'given of opposite motions in muscles ? Describe the 
muscles represented in Fig. 56, ahd explain their operation. 



THE MUSCLES. 



i:j5 



Fig. 56. 




projection there. Fortius 
purpose, it is shaped very 
differently from the mus- 
cles of the arm in Fig. 55. ^ 
There are some other mus- 
cles in this figure, which *' 
I will barely notice. — 
There is at (2 a small mus- c 
cle, which, coming from 
the bone at the top of the 
nose, is fastened to the 
skin of the eye-brow. — 
When it contracts, it 
wrinkles the eye-brow. — 
At ^ is a muscle that 
draws up the corner of 
the mouth, and at / is a muscle that draws down 
the lower lip. At (i is a muscle which serves several 
purposes. It pulls back the corner of the mouth ; and 
Avhen we are eating, By pressing the food towards the 
middle of the mouth, keeps it from getting outside ot 
the teeth. "When one blows upon an instrument 
strongly, this muscle gives firmness to the cheek, so 
that the air shall not press it out too much. From 
its doing this, it is called huccinator^ from huccinare^ 
to blow a trumpet. 

10. At A, in Fig. 56, you see a long muscle, which 
begins just behind the ear, and goes down to the top 
of the breast-bone. You see another muscle on the 
other side of the neck exactly similar to it. This pair 
of muscles is very plainly seen in the neck of a thin 

Explain the action of two muscles in the neck in bowin": the head 



1^6 FIRST BOOK IN PHYSIjLOGY. 



person. When they contract together, you bow tlie 
head forward. If they contract exactly alike, you 
bow your head straight forward. But if one of them 
acts more than the other, then you bow your head in 
a one-sided way. If you observe persons as they bow 
to those whom they pass, you will see that they often 
bow more or less in a one-sided way. That is, one of 
these muscles pulls upon the head harder than the 
other does. In some, this unequal action of this pair 
of muscles becomes a habit. 

11. Observe now what a variety of motions can be 
produced by these two muscles alone. First, the 
extent to which you bow the head forward can be 
varied to any degree you please, by varying the 
degree of the contraction of these muscles. When 
you bow your head forward very much they contract 
strongly ; and when you bow it forward but little 
they contract slightly. And their contraction can 
vary in all degrees between the greatest and the 
slightest. So also the direction in which the head is 
bowed can be varied to any extent you please. You 
can bow the head in any direction, either to the right 
or left, by varying the inequality of the action of iht 
two muscles. If you bow your head very much to 
one side, you make one of them contract much more 
strongl}^ than the other. But if you incline the head , 
only a little towards one side, the muscle of that side 
contracts only a little more than that of the other side. 
And the inequality in their contraction can be varied 
in all degrees between the smallest degret and the 



Show the variety of motion that can be made by therL lo two wnya 
— in regard to the extent and the direetion of the motion. 



THE MUSCLES. 137 



greatest. You will realize the truth of what I have 
told you in this paras^raph, if you try the experiment 
on yourself, and observe how much you can vary the 
bowing of your head both in extent and direction. 

12. Now, if so much variety of motion can be pro- 
duced by only two muscles, how great is the variety 
when there are many muscles in action, each of which 
can have its contraction varied in all degrees. You 
see this well illustrated in the hand and arm. Raise 
your hand, and think what the muscles do when you 
perform this motion. Although it seems to you so 
simple a motion, many muscles are engaged in per- 
forming it. And each one of these muscles has its 
particular part to do in making the motion. In doing 
its part it must contract just enough. If it pull too 
much, or too little, it will interfere with the action of 
the other muscles, and there will be a failure in the 
motion. But there is no such failure. All the mus- 
cles contract just enough, and the hand is raised 
exactly as the mind directs. Now, if you raise it 
again in a little different position, all these muscles 
act in a little different way. And you can go on to 
raise it in a great variety of ways, altering the height 
and direction each time by altering the action of all 
these muscles. 

13. At the same time that you vary the motion of 
the hand, you can also vary to almost any extent the 
motions of the fingers, by the varied action of the 
muscles that work them. You can get some idea of 



What is said of the variety of motion when many muscles act u» 
gether? Ulustrnte by referring to the hand. What is said of tbj 
axact manner in which each musc^^ does its part? 



138 FIRST BOOK IN rHYSI0L0C4Y 

the variety of these motions if you watch a person 
that is writing, or one that is playing on a piano. For 
every one of these exceedingly varied motions there 
must be a variation of the action of a great number 
of muscles. Each muscle must in every motion per- 
form its particular part exactly right, or there will be 
an interference with the action of the other muscles; 
and consequently a failure in the motion. But, com- 
monly each muscle contracts exactly right, and so 
each one of the motions that so rapidly follow each 
other is performed just as the mind directs. 

14. If you examine some of the motions performed 
by the fingers, that appear very simple, you will see 
that they are performed by a very complicated ma 
chii'cry. Take, for instance, that seemingly simple 
movement made in buttoning your coat. If you 
watch the fingers, as they put the button through the 
outton-hole, you will see that the movement is quite 
a complicated one. It is so much so, that no man 
could make a machine in the shape of the hand that 
could perform it. And the same can be said of other 
motions. 

15. The tongue exhibits great variety in its motions. 
Lf you stand before a glass, and, opening your mouth, 
move about your tongue rapidly, it looks as if some 
little tricksy spirit were in it playing on its fibres. 
But each of these fibres is put exactly in its right 
place, and contracts exactly aright in all the varied 



What is said of the variation of the motions of the hand and fingei-s 
m such actions as writing, or playing on a piano ? What is said of 
Bo«ae apparently simple motions of the fingers? What is sa/d of the 
IT ( vements of the ton^u?, and of the arrangement of its fibres 2 



THE MUSCLES. 13S 

motions of this organ, as we use it in speaking, and 
eating, and swallowing. 

16. The act of swallowing seems to you a very 
simple thing, but it is really a complicated act of a 
complicated set of machinery. There are many 
muscles that work together in doing it, and if they 
did not work right there would be failure in the 
motion, and choking would result. Observe that dif- 
ferent muscles work in diflFerent parts of the act. 
When you first begin the act, the food is thrust back 
chiefly by the muscles of the tongue. As it goes 
back, the epiglottis, the lid of the larynx, is shut 
down by its muscles, so that the food may slide over 
it into the oesophagus that lies behind the windpipe. 
This lid, which thus shuts over the top of the passage 
to the lungs when we swallow, is raised up by its 
muscles when we speak or breathe. It is like a little 
tongue extending back from the root of the tongue 
itself. After the food has passed over this lid it goes 
down through the oes'ophagus into the stomach. But 
it does not simply fall down. The oesophagus is a 
tube, made in part of muscular fibres, so arranged 
that the food is really pushed by their action through 
this tube. So complicated is all this machinery, and 
so nice is its operation, that it would be impossible 
for any man to make a machine of the same shape 
that could perform the act of swallowing. 

17. It seems to you a simple thing to speak. Bin 
every time that you speak there is a large number of 
muscles brought into action. There are the muscles 

What is said of the act of swaUowiDg? Describe the different parti 
of* this act. 



140 FIRST BOOK IN PHYSIOLOGY 

of the chest that force the air out through the wind 
pipe — the muscles that move the cords in the music- 
box, the larynx — the muscles that move the epiglot- 
tis, the lid of the larynx — and the muscles that move 
the palate, the tongue, the jaws, and the lips. You 
cannot utter a word without tlie action of all these 
different muscles. And they must act just right, or 
there would be something wrong in the sjund of the 
word. 

18. As the different acts of speaking, laughing, 
breathing and swallowing follow each other so rapidly, 
there is vast variety in the changing action of the 
muscles. Especially busy are those little muscles that 
work the lid of the larynx, opening it when we 
breathe, or speak, or laugh, and shutting it down 
when we swallow. So securely do these door-keepers 
guard this door to the windpipe, that it is a rare acci- 
dent for a crumb or a drop to get into it. 

19. In performing the different motions that I have 
alluded to, such as swallowing, speaking, and the mo- 
tions of the hand, there must be a concert or agree- 
ment of action among the muscles. The concert is 
as real as it would be if the muscles, like men that 
are pulling at ropes, understood each other, and agreed 
together as to what they would do. It is, indeed, a 
more perfect concert of action than ever occurs 
among a company of men in pulling ropes, especially 
when they pull upon different ropes. It is difficult 

What different sets of muscles are engaged in the act of speaking!* 
What IS said of the variety of muscuhir action as we speak and breathe 
and laugh and swallow almost at the same time? What muscles are 
then especially busy? What is said of tlie concert of action in tlie 
muschis ? 



THE MUSCLES. Hi 



for each man to pull just enough and at exactly the 
right time. But there is no difficulty of this sort 
commonly with the muscles, however complicated 
the action may be. Thus in swallowing, each muscle 
acts just strongly enough and exactly at the right 
time. 

20. I will now give you a general view of the mus 
cles of the body. In Fig. 57 you have a side view of 
the muscles, that is, of all those that lie directly under 
the skin. There are many other muscles that lie un- 
der these that you see. You observe that the muscles 
are of various shapes and sizes, according to their 
situation and what they are intended to do. They are 
round, flat, long, short, fan-shaped, circular, &c. I 
will notice some of them particularly. 

21. At (^ is a very large muscle at the top of the 
shoulder, that raises the arm, at the same time carry- 
ing it out from the body. At h is the muscle that 
bends the fore-arm at the elbow. At e is the muscle 
that acts in opposition to h and straightens the arm. 
The muscles at h and e are the same as those at 4 and 
7 in Fig. 55. At 6? is a muscle that turns the fore- 
arm in such a way that the palm of the hand is up- 
ward, as seen in the figure. At p' is a very large mus- 
cle. It comes from almost the whole length of the 
back-bone, and its tendon is fastened to the back part 
of the arm. Its office is to draw the arm back. Its 
tendon makes the rear boundary of the arm-pit. At 
I is one of the large, flat muscles of the abdomen. At 
I and h are two muscles that move the thigh. At o 

Describe rue muscles of the body as represented in Fi^ fi^ 



142 



FIRST BOOK IN PHYSIOLOGY 



Fio. 57. 




and p on the right thigh, and at n on the left, are seeii 
three muscles that serve to throw the leg forward 
They do this by pulling on the knee-pan. At q is thf 



THE MUSCLES. H3 

tendon that forms the outer hamstring, and at r are 
the two tendons that form the inner one. The mus- 
cles that pull these hamstrings are on the back part 
of the thigh. When they act they make the leg 
swing backward, and therefore do just the opposite of 
what is done by the muscles n^ o and p. At s is the 
muscle that makes the back of the calf of the leg. Its 
strong tendon, which is fastened to the bone of the 
heel, you can feel very plainly through the skin. It 
is this muscle, a part of which is represented in Fig. 
54, at p. 

22. The muscles differ greatly in size. Some are 
very large, and some are exceedingly small. Con- 
trast, for example, the muscles of the arm that wield 
the hammer and the axe, with the muscles that move 
the cords of the larynx in speaking and singing. 
These muscles of the voice are very delicate, and they 
produce the various notes by motions so small, that 
many of them could be measured by the breadth of 
a hair. Birds that mount up so beautifully in the air, 
have large muscles to work their wings. But the 
muscles that move their little musical cords, as they 
carol so sweetly, are so small, that it is difficult to find 
them when we dissect the larynx. 

I will now notice some especial contrivances in the 
muscles and tendons. 

23. There is a beautiful arrangement of the ten- 
dons in the toes and the fingers. In Fig. 58 is a rep- 
resentation of this arrangement in one of the fingers. 
At a, h and c^ are the three bones of the finger. Aty 

What is said of the size of the muscles? Give the contrasts men 
tioned. 



144 KIRST B0O7. IN PHYSIOLOGY. 




i 

IS the fceiv.d^n that bends the second bone, h. This i« 
divided into two parts, as you see, just at its end 
where it is fastened to the bone. Through this divi- 
sion the tendon e passes, to go to the last bone, c. Ie 
the Figrre the tendons are raised up so that you may 
see the arrangement clearly. This arrangement is 
seen ir. each of the fingers and in each of the toes. 

24. There b a very curious contrivance in the sole 
of tho foot. There is a muscle in the calf of the leg, 
from, which there comes dov/n a tendon that is divided 
into lOur, for the purpose of bending the toes. Now, 
tl:ere is a short muscle in the bottom of the foot that 
sends four tendons to join those that come down from 
the muscle in the leg, so as to help them pull the toes. 
The reason for this arrangement is this. If all the 
muscle that is needed to pull the toes were to be put 
into the sole of the foot, it would make the foot too 
large at that part; so the thing is done with two mus- 
cles, put in different places, instead of one muscle. It 
is the same sort of contrivance with that to which a 
man would resort, if he wished to move something 
with ropes, manned by a company of men, but could 
not conveniently get men enough into one spot to do 
it. He would fix some other ropes in another spot, in 

Describe the arrangement of tendons represented in Fig. 58. Describe 
the arrangement of muscle and tendons in the%sole of the foot. Give the 
comparison made in regard to it. 



THE MUSCLES. 145 



such a wa)^ that a second company of men could help 
the first. This short muscle in the sole of the foot has 
received the sino^ular name of onassa carnea Jacohi 
Sylvii — that is, the fleshy mass of James Sylvius, the 
anatomist who first pointed out this arrangement, 

25. We have many examples of tendons working 
with a pulley-arrangement. This is the case with the 
tendons that go from the muscles in the leg to the 
foot. They are bound down by ligaments at the 
ankle, and work under them, just as a rope works 
through a pulley. If it were not for these ligaments 
the tendons would fly out continually when the mus- 
cles acted, making projecting cords under the skin. 
There are similar ligaments at the wrist. 

26. There is a beautiful example of the pulley- 
arrangement in the eye, which you see in Fig. 59 

Fig. 59. 




There are six muscles that move the eye-ball. Five 
of them are represented. There are four straight 
muscles. Three of them are marked <z, 5 and c. You 
see just the upper edge of the fourth one behind b. 
These muscles come from the back part of the socket 
of the eye, and have tendons that are fastened to the 

"VThat is the puUey-arrangenient at the ankle aud wrist ? Describe 
the muscles of the eve-ball as given in Fig. 59 

7 



146 



FIRST BOOK IN PH YSI OLOir Y". 



eye-ball. The muscle a^ when it contracts, turns the 
eve upward ; c turns it downward ; & turns it to one 
side, and its opposite muscle turns it to the other side. 
But there are some other roUinp; motions of the eye 
that are performed by two oblique muscles, as they 
are called. One of these, 5, is represented. It has a 
long tendon, w^hich passes through a ring in the car- 
tilage in the roof of the socket, and then turning 
back is fastened, as you see, to the upper part of the 
eye-ball. 

Fio. 60. 




27. I will notice one more example of the applica- 
tion of the pulley. It is in the case of the muscle 
that draws down the lower jaw, represented in Fig. 
60. It is in reality two muscles. One, a^ is attached 
to the bone behind the ear, and the other, 5, is 
attached to the inside of the chin. They join together 
by a tendon ; and this tendon, as you see, works in a 
loop, as a rope does in a pulley. You can see that 
when these two muscles, a and J, contract, they draw 

Describe the aiTaogemeDt of the muscle that pulls down the ""owe)- 
iaw. 



THE MUSCLES. H7 

down the jaw. Now observe, that the jaw could be 
drawn down in a mucli more simple way than this. 
It could be done by a muscle going straight from the 
chin to the top of the breast-bone. But this would 
make the neck look very ugly, and hence this pulley- 
arrangement was adopted. The machinery that 
draws down the jaw is in this w^ay kept out of sight, 
and so does not interfere with the beautiful shape of 
the neck. 

28. This regard to beauty of shape, so manifest in 
the arrangement of this muscle in the neck, may be 
observed in the arrangement of the muscles generally. 
They are so arranged, for example, in the limbs, as 
to give to them a graceful shape. The muscles 
which move the hand and the fingers are mostly 
placed in the arm, giving to it the full and flowing 
outline wdiich makes it so beautiful. If they were 
placed m the hand, where they do their work, tho 
hand would be a very clumsy instrument. I could 
give many other examples, but these are sufficient. 

29. You see that there are in the body, in its two 
halves, two sets of muscles that are alike, just as it in 
with the two halves of the brain and the two sets of 
nerves. The exact equality of the two sets of muscles 
is strikingly exemplified in the muscles of the mouth. 
The mouth is held in the middle of the face, because 
the muscles on each side of it are exactly alike, and 
pull alike upon its two corners. If the muscles on one 



What is the need of this peculiar aiTaogement ? What is said of re- 
gard to beauty in the arrangement of the muscles ? What is said of the 
two sets of muscles in the two halves of the body ? How is the mouth 
held in the middle of the face f 



148 FIRST BOOK IN PHYSIOLOGY. 

side were stronger than those on the other, the mouth 
would be drawn to the side of the strongest. Some 
times the muscles on one side of the face are palsied, 
and then the mouth is drawn to the other side. 

30. When the face is palsied upon one side, the 
two kinds of contraction that I noticed in § 3 are well 
illustrated. When the muscles of the face are quiet, 
the difference between the two sides is not very great. 
For the muscles are then ojnly under the influence of 
their elasticity, and this is not much less in the pal- 
sied muscles than in the opposite ones. But the 
moment that the muscles are excited to contraction 
by the nerves, as in speaking or laughing, the mouth 
is drawn very much to one side, giving the face a 
very odd appearance. 

81. Sometimes muscles are for some reason perma- 
nently contracted, and thus cause deformity. Squint- 
ing is produced in this way. The straight muscle on 
one side of the eye-ball contracts more strongly than 
the straight muscle on the opposite side. Thus, if the 
eye turns in towards the nose, the inner muscle con- 
tracts more strongly than the outer one. 

32. The expression of the countenance depends 
entirely upon the action of muscles. The chief of 
these muscles of expression are those that wrinkle the 
eye-brows, and those that pull up and pull down the 
corners of the mouth. When one laughs, the corners 
of the mouth are drawn up, as seen in Fig. 61. But 
when one cries or is very sad, the corners of the 

What is said of the two kinds of contraction when the face is palsied 
on one side ? How is squinting produced ? Upon what does the ex- 
pression of the countenance depend ? What muscles are the chief agents 
uf expression ? 



THE MUSCLES 



149 



FiG. Gl. 




moutli are drawn down. In laughing, the muscles 
draw up the corners of the mouth so strongly as to 
push up the cheeks and wrinkle the skin under the 
eyes; but in smiling, the muscles raise the corners of 
the mouth but slightly. The eyes seem to smile, but 
they do not. It is the effect wholly of the action of 
the little muscles that raise the corners of the mouth. 
33. In Fig. 62 there is an action of the muscles of 
expression entirely different from that in Fig. 61. 
Here is an expression of jealous, peevish melancholy. 
The corners of the mouth are drawn down, and the 
eye-brows are wrinkled by the muscle ^, repre- 
sented in Fig. 56. This makes the eyes look cross. 
N"ow, if the eyes remained just the same, and the 
n.uscles that wrinkle the eye-brows and those that pul) 

Explain the action of the muscles iu Figs. 61 and 62. 



150 FIRST BOOK IN PHYSIOLOGY. 



Fig. 62. 




down the corners of the mouth were relaxed, the ejan 
would look pleasant. This subject of the expression 
of the countenance I treat in full in my larger work 
on Physiology. 

34. I have spoken mostly of those muscles that act 
in obedience to our w^ill. These are called voluntary 
muscles, and they are excited to act through nerves 
that come from the brain. The muscles of our limbs, 
^br example are excited to act throu.2:h the nerves 



THE MUSCLES. 151 

that come to them from the brain when the mind 
wills them to act. But there is another class of mus- 
cles that act without our willing them to do so. They 
are called involuntary muscles. The heart, for exam- 
ple, is a bundle of muscles, that are always acting 
without being told by the mind to act As the stom- 
ach churns the food, as mentioned in § 13, in Chap- 
ter UL, the will has nothing to do with the contrac- 
tion of its muscular coat. And so the muscles of 
breathing keep at work without being told to do so by 
the will. 

35. These involuntary muscles, then, are parts ol 
the muscular machinery that do not depend upon the 
mind to make them act. They act when the mind is 
asleep as well as when it is awake. While the volun- 
tary muscles are resting, some of the involuntary 
muscles are ever at work. The heart is always pump- 
ing the blood, and the muscles of breathing are always 
working the chest to bring fresh air into the lungs. 

36. You see at once the reason why such muscles 
are involuntary. If they were voluntary, the mind 
would have to attend to them all the time to keep 
them at work, for life would cease if the respiration 
and the circulation stopped. The mind, therefore, 
not only could not have any time for sleep, but it 
would have every moment occupied with keeping the 
circulating, breathing and digestive machinery m 
operation, and could not attend to any thing else. 
But as it is, all this machinery keeps at work continu- 

What is the difference between voluntary and involuntary muscles \ 
Give examples of both kinds. What is their difference as to restin^W 
Why are tts heart and the muscles of respiration involuntary? 



152 FIRST BOOK IN PHYSIOLOGY. 

ally without any superintendence on the part of the 
mind, except the attention that is required to supply 
the digestive machinery with its material, the food 
that we eat. 

37. But the muscles of the respiration are not 
wholly involuntary. Although they commonly work 
without the mind's superintendence, the mind can 
regulate their action to some extent. We can, for 
example, breathe quicker or deeper than usual if 
we wish to do so. But though the mind can regulate 
the action of the breathing muscles, it cannot wholly 
control it. No one can stop his breathing, as he can 
stop walking, by simply willing that it shall stop. 

38. Now, there are two reasons why the mind has 
this partial control over the muscles of respiration. 
The first is, that it uses them in certain acts, as speak- 
ing, singing, blowing, &c. Auother is, that the mind 
needs to direct in their use when the lungs are in any 
way embarrassed. So long as there is no difficulty, 
the breathing is performed by the muscles involunta- 
rily, without any superintendence from the mind. So 
long as the mind feels no inconvenience it scarcely 
ever spends even a thought upon the breathing. But 
as soon as there is embarrassment there is a disagree- 
able sensation — that is, the mind is informed of the 
embarrassment through the nerves. It, therefore, at- 
tends now to the breathing machinery, in order to 
have the breathing performed in the best manner 
possible. For example, when a man is suffering with 

How much are the muscles of respiration influenced by the wiU 
What two reasons are there for this? How much notion does thfl 
mind take <)i tlie working of tlie nrachinerj of ]'espirati^~»^ ' 



THE EYE. 153 



asthma, the mind directs the use of the muscles of the 
chest, so as to get as much air as possible into the 
lungs. But when the asthma is gone, the mind ceases 
to superintend these muscles, and the breathing goes 
on again by their involuntary action. 

39. While the muscles of respiration are both 
vohintary and involuntary in their action, the heart is 
wholly an involuntary muscle or set of muscles. No 
one can make his heart beat more quickly or more 
slowly by determining that it shall. He may do it 
by exercise, or by thinking of exciting subjects, but 
he cannot do it by any direct action of the will 



CHAPTER X. 

THE EYE. 



1. The eye is one of the principal instruments that 
the mind uses in getting a knowledge of the world 
around it. Though it is a small organ, it is a very 
complicated set of machinery. It has many struc- 
tures in it diftering much from each other, as you will 
see as I proceed. It has six nerves, as I have before 
told you, and four of these are the nerves by which 
the mind works the muscular machinery of this organ. 

2. You will see, in this chapter, that the eye is 
an optical instrument. It is, therefore, constructed 
Bomewhat like the optical instruments that man makes, 

Is the heart in any meas ire a voluntary muscle ? What is said ol 
the structure of the eye? What k^id of instmment is it? Wliat in 
^truments is it like ? 
7^ 



154 FIRST BOOK IN PHYSIOLOGY. 



but is much more perfect. For example, it is like a 
telescope, and it is also like a camera-obscura. And 
i shall show you, that in some respects it is like the 
instrument used in taking daguerreotypes. 

3. The eye is contained in a deep bony socket, 
which you see in Fig. 41, on page 111. As you look 
at the eye you see only its front, with a portion of its 
sides, as it rolls in its socket. It is in shape like a 
globe, but it is not perfectly round. Its front part, 
w^here the clear w^indow is, stands out a little. The 
eye has a complete case enclosing all its soft and deli- 
cate parts. But this case is not all alike. It has two 
parts w^hich are very different from each other. There 
IS a thick white part called the sclerotic coat, from a 
Greek word, meaning hard. It is what is commonly 
called the white of the eye. It is this coat that gives 
the firm feeling to the eye when you press your finger 
upon it. But this coat does not extend over the front 
df the eye. There is there, as you see, a clear trans- 
parent part of altogether a diflferent structure. This 
[its into the white coat very much as a watch-glass fits 
}nto the case. It is called the cornea. 

4. Looking through this window of the eye, you see 
I little behind it a delicate colored curtain, called the 
tris, with a round opening in it called the pupil. The 
tris is difi'erently colored in diflferent persons. And 
we call the eye blue or brown or gray, &c., according 
to the color of this curtain. Through the pupil we 
look into the very inner chamber of the eye. This 

What is the situation ^f the eye ? What is its shape? What is the 
Bclerotic coat? What is the cornea? How does it fit into the sclerotic 
coat? What is the iris ? What is the pupil of the eye ? Into "what dn 
we look through t) e pupil ? 



THE EYE ^•'>5 



always lias a dark appearance, because, as you will 
Boon see, this chamber has a lining of a dark color. 

5. The iris makes the eye very beautiful. But it is 
not a mere ornament. It is an important part of the 
machinery of the eye. Its chief office is to regulate 
the quantity of light that goes into the eye. You caii 
see how this is done. If you look into the eye of any 
person while you hold a light at some distance, you 
§ee that the pupil is quite wide open. Now bring 
the light near the eye, and you will see the pupil in- 
stantly grow smaller. This is because the iris or cur- 
tain has contracted its opening in order to keep too 
much light from going into the eye. In the glare of 
a bright sun this opening tnat lets in the light becomes 
very small ; but in the dark it is very wide open, be- 
cause the eye then needs all the light that it can get. 

6. I will now explain the way in which the iris 
acts in regulating the quantity of light that enters the 
eye. The iris has two sets of fibres, straight and cir- 
cular. These are represented in Fig. 63. In a the 
pupil is wide open. Here the ^^^- ^'^• 
circular fibres are relaxed, and 
the straight ones are contract- 
ed. In h the pupil is contract- 
ed. And here the fibres are 
just the reverse of what they are in a — the straight 
ones are relaxed and the circular ones are contracted. 

7. The fibres of this round curtain must be very 
nicely arranged, and be made to act with great exact- 
ness ; for the iris is always perfectly even as it en- 

What is the chief use of the iris? How would you show its use! 
ExpUiin the rnanoer iu which the iris acts. 




156 FIRST JiOOK IN PHYSIOLOGY. 

larges or contracts its opening, and there are never 
any wrinkles in it. If any person should attempt to 
construct a curtain after this form, with a round open 
ing in it, he could not in any way fix the strings by 
which the opening would be made smaller or larger, 
so as to keep the curtain always smooth and its edge 
always regular. 

8. I will now give you a more full and particu- 
lar description of the parts of the eye. In Fig. 64 
you have a map of the eye. It has three coats ^ as 

Fig. 64. 



CL T) 

they are called. At a is the thick, strong, wliite 
coat, the sclerotica. Into it the cornea^ e^ the clear 
window of the eye, fits, as I have before told you, 
like a crystal of a watch in the case. These two 
parts, the cornea and the sclerotica, really together 
make one coat. Inside of the sclerotic coat is the 
cJwroid coat, 5. This is of a dark color. Why 

What is said of the regularity of action of the iris? Describe th<» 
parts of the eye as represented 'n Fig. 64. 



rilE EYE. 15T 



this is so 1 will tell you in another place. At c is the 
retina. This is very thin, and is chiefly comj)osed ot 
the fibres of the optic nerve, d, that enters the eye at 
its back part. 

9. The eye has three Jiumors^ as they are called. 
There is the aqueous^ or watery humor,/*, in the front 
part of the eye behind the cornea. The iris, g g^ is in 
the midst of this humor. It divides the chamber that, 
contains the humor into two parts. The part of the 
chamber which is in front of the iris is, as you see, 
much larger than that which is behind it. At h is the 
crystalline humor, or lens^ as it is more often called. 
This lens is a substance like hard clear jelly. Then 
behind this, filling up all the space, i, is the vitreous^ 
or glassy humor, which is like soft jelly. You see 
that it is this vitreous humor that fills up a great por- 
tion of the ball of the eye. 

10. The object of all this apparatus that I have de- 
scribed is to have images of objects formed upon the 
retina^ c. That these images are formed there can 
be proved by an experiment. Take an ox's eye, and 
peel off* carefully the thick rind at the back part, thai 
is, the sclerotic coat, so that very little but the retina 
is left. If now you hold a candle before it, you can 
see the image of the candle on the retina at the back- 
part of the eye. So, if you place it in a hole in the 
window-shutter, the images of objects, such as houses. 
trees, &c., can be seen pictured on the retina. 

11. This picturing upon the retina takes place with 
eyery object that w^e see. If we look at a single ob- 

W'hat is the object of the apparatus of the eye? How can you prov< 
ihat imni^es are formed on tlie retir i ? 



15S FIKST BOOK IN P H Y S I L G V, 



ject, as a candle, its image is formed distinctly in tli(-. 
back part of the eye. And so, also, if we look at a 
wide prospect, all the multitude of objects that we see 
are pictured there in a space that a sixpence would 
cover. 

12. I will now explain to you in what way these 
pictures are formed upon the retina. It is the light 
that forms them. The rays of light that come from 
the sun are reflected from every object in all direc- 
tions. And when you see an object, it is because 
these rays reflected from it enter your eyes, and make 
its image in them. For example, when you see a 
tree, the light which is reflected from the tree passes 
into the window of the eye, and pictures out a tree on 
the retina. 

13. In this formation of the pictures of objects on 
the retina, the eye is like the instrument called the 
camera-obscura. In this instrument there is a dark 
chamber into which light is admitted through glasses 
.n a tube. The light that thus comes in, pictures in 
the dark chamber of the instrument the trees, houses, 
and other objects that are in front of the tube. And 
as you look into this chamber through an opening, 
you see the picture. That dark chamber in the eye, 
that is filled with the vitreous humor, is like the dark 
chamber of the camera-obscura, and the lenses and 
humors of the eye serve the same purpose as the 
glasses in the tube of this instrument do. 

14. In this formation of pictures of objects, the eye 
is also like the instrument used in taking daguerreo- 

In Avhat way are the images of objects pictured od the retina f 
Trace the resemblan ^e of the eye to the camera obseiira. 



THE EY E. 159 

lypes. When your daguerreotype is taken, the rays 
uf light that shine upon your face are reflected or 
thrown off from it into that round window that you 
look at in the instrument. These rays enter through 
this window into a dark chamber, just as they do in 
the camera-obscura, or in the eye, and picture your 
image on a plate of metal there. This plate of metal 
is to this instrument w^iat the retina is to the eye. 

15. The metallic plate in the daguerreotyping 
instrument differs from the retina in one important 
respect. The image made on the retina does not 
remain, but that which is formed on the metal does. 
The surface of the metal is prepared in such a way 
that the image made by the light is left there. It is 
a beautiful idea that light should thus be the pencil 
to paint your picture. And yet, whenever any one 
looks upon you, the light paints your picture in his 
eyes upon the retina, just as it does upon the metallic 
plate in the daguerreotyping instrument. Indeed, 
every object that is seen, is for the moment daguerre- 
otyped upon the retina. And as you look at object 
after object, there is a constant succession of pictures 
made there. 

16. The eye is in some respects like a telescope. It 
has lenses like this instrument. The pro fig. 65. 
jecting cornea in front acts as a lens. But 
the principal lens of the eye is tlie crystal- 
line lens, which is represented in Fig. 65. 
The rays of light are brought nearer together 

How does the eye resemble the daguerreotyping insti'ument i What 
s the difference between the picture on the retina and that on the plait* 
)f metal in the daguerreotyping instrument ? How is the eye like a 
lelesoope 'i 



160 



FIRST BOOK IN PHYSIOLOGY. 



by the lenses of the eye, just as they are by the lenses 
of the telescope. 

17. The lenses and humors of the eye must be very 
exactly arranged, in order that the sight may be per- 
fect. They must be so arranged that the images ol 
objects shall be formed distinctly on the retina. Now in 
near-sighted persons the lenses and humors are so ar- 
ranged as to'make the rays that form the images come 
together too quickly, before they reach the retina. This 

Fig. 66. 




Fig. 67. &^ 



IS represented in Fig. ^Q. The result is, that a contu- 
sed instead of a clear image is formed on the retina. 
If the retina could be brought forward to where the 
figure of the cross is represented, the image would be 
clear. The common remedy for the near-sighted is a 
glass, that has an effect upon the rays of light 
the opposite of that which is produced by the 
cornea and the crystalline lens — tliat is, a glass 
which separates the rays instead of bringing 
them nearer together, and so prevents the rays 
from coming together in the eye too soon. 
Such a glass is called a concave lens. Its two 
sides are hollowed out more or less, as represented in 
Fig. 67. The crystalline lens, seen in Fig. 65, is, on 
the other hand, a convex lens. 

What is said of the arrangement of the lenses and humors of the ey?? 
What is the difficulty in the near-sighted \ What is the remedy ? 



THE EYE. 1^1 



18. That large rear chamber of the eye, where the 
images of objects are pictured on the retina, I have 
told you, is a dark chamber. It is made so by a 
coloring substance which is in the choroid coat. If 
it were not dark our vision would be indistinct, from 
the glare of light in the eye, just as it is when we go 
into a room where the walls are all of a very light 
color. In the albino there is none of this coloring 
matter in the choroid coat, and therefore he cannot 
see well in a bright light. Some animals, that use 
their eyes only in the night, have none of this dark 
matter in them, because it is only needed when the 
bright light of day is shining into the eye. 

19. I have thus shown you how the images of 
objects that we see are pictm^ed in the retina. But 
this is not all the process that we call seeing. There 
is something more needed besides the formation of 
these images, in order to have the mind see the 
objects. Now the mind does not look into the dark 
chamber where the images are, as we look into the 
chamber of the camera-obscura. The mind gets a 
knowledge of the images in a different way from this. 
It gets it by means of the optic nerve, the end of which 
spread out forms the retina. The images pictured 
there make impressions on the net-work of the nerve, 
and these impressions go to the brain by this nerve, 
and the mind feels them. In regard to the use of the 
word impression^ in speaking of the operation of the 



What is the cause of the darkness of the large rear chamber of th« 
«ve ? Why is it made dark ? How is it in the albino ? How is it in 
Bome arjraals? In what way does the mind get its knowledge of th* 
images made oj> th? ^^etina ? 



162 FIRST BOOK IN PHYSIOLOGY. 

nerves, 1 refer j^ou to what I have said in the chapter 
on the nervous system, § 20. 

20. The eye may be in perfect order, so that the ima- 
ges of objects may be pictm^ed accurately in its dark 
chamber, and yet there may be no seeing. For the 
nerve may not be able to pass the impressions on to the 
brain. A tumor, for example, may press on it so that 
nothing can pass through its little tubes. It is by 
means of the nerves, then, that the mind makes use 
of its optical instruments, just as is true of all the 
other apparatus or machinery of the body. 

21. There is one thing ver}^ curious in regard to the 
pictures formed on the retina. They are always 
inverted or upside down. If you look at a man, for 
example, he is pictured on your retina with his head 
down. And so of every object. Accordingly, in Fig. 
f)6 the image of the cross in the eye is represented 
upside down. But although the images of objects 
are thus reversed on the retina, your mind sees every- 
thing right-side up. How this is we know not, but in 
Bome way the matter is so fixed in the brain or the 
nerves, that the right impression goes to the mind. 

22. Observe another thing. There are two eyes. 
Of course there are two images of every object that 
you see, and two impressions are carried by the twe 
optic nerves to the brain. And yet the mind receives 
but one impression, and so sees but one thing. This 
is because the two eyes are alike, and work alike. If 
this were not so, there would be confused and double 



What is said in regard to the optic nerve as being necessary to see- 
ing ? What is said of the position of the images on the retina? What 
'e said o^ the fact that we have two eyes? 



THE EYE. 16S 



vision. If the eyes were not alike throughout, the 
pictures in the two retinas would not be alike, and 
two different impressions would be sent by the two 
nerves to the brain, and then you would always see 
two things instead of one — two faces, two trees, two 
houses, and so on. So also, if the muscles of the eyes 
did not work alike you would see double. For this 
reason, if you press your finger on the side of one eye, 
you see everj^thing double ; for you keep the two 
eyes from moving together as they usually do. 

23. There are several reasons for our having two eyes 
or optical instruments for the mind to use, instead of 
one. You could not look in so many directions with but 
one eye. You do not use both eyes together all the 
time, but you use one or both, as you find most con- 
venient. Then again, if you lose one eye by any 
accident, you have another. And we cannot conceive 
of any way of placing a single eye in the face so as 
to look as well as two eyes do. 

24. The eye is a very tender, and at the same time 
a very important organ. It is, therefore, very care- 
fully guarded against injury. Observe, how the 
bones jut out all around it; the bone of tlie fore- 
head, that makes the projecting roof of the socket, 
the cheek-bone, and the bones of the nose. These 
parapets of bone are so arranged that they receive 
almost all the blows that are aimed at the eye. The 
eye is therefore seldom injured, except by something 
tlirust straight into it, so as to avoid these jutting 

How is it, that with two eyes our vision is not confused or double! 
vV^hat reasons can be given for our having two eyt^s? How are tha 
'jones abou<- the eye arrancred so as to guard it? 



/64 



FIRST BOOK IN PHYSIOLOGY. 



walls around it. Then, top, the eye has a cushion oi 
fat, and does not lie against the hard bone of thf« 
socket. Now, if the eye sees a blow coming, the 
muscle that makes the motion of winking shuts the 
lids, and pushes the eye back against this soft cushion. 
This, of course, not only covers it up, but sinks it 
deeper between the parapets of bone, and so puts it 
more out of the reach of the blow. 

25. The eyelashes serve to keep light things, fljing 
in the air, from entering the eye. The muscle that 
so quickly shuts the eye-lids, however, does more at 
this business of keeping out intruders. The eye- 
brows, besides being an ornament, are of some use as 
a protection. If they were not there, the perspiration 
on the forehead would continually run down into the 
eye, and would irritate and inflame it. The eye- 
FiG. 6s. brows are the eaves of 

the roof of the eyes' hab 
itation, and the perspira- 
tion drops from them 
upon the cheek below. 

26. There is a beauti- 
ful apparatus for moist- 
ening and washing th-e 
eye. The tear-gland, 
that makes the wash for 
the eye, is situated above 
the eye, a little toward 
it:^ outside, as repre- 




Does the eye lie directly against the bone of its socket? What is 
done when the eye sees a blow coming? How is the eye protected by 
the eye-lashes? How by the muscle of the eye-hds? How by th^ 
eye-browa ? 



THE EYE. 16b 



sented at a^ in Fig. 68. The tears are carried from this 
factory by little ducts, as seen at J, and are poured over 
the surface of the eye. They serve to keep the eye moist, 
so that it can be moved about in its socket easily by 
the muscles. They also serve to wash out substances 
that get into the eye, and when they are needed for 
this purpose the tear-gland makes them abundantly. 
Fishes have no tear-gland, for the water m which 
they live answers the purpose of tears in their case. 
Neither have they any eye-lids, as they are not expo- 
sed to dust, or motes, or flying insects, as animals that 
live in the air are. For the purpose of moistening 
the eye, the tears come from the gland in a small 
amount all the time. Of course, there must be some 
contrivance for the passing off of the tears, or they 
would continually run over the edges of the lids. 
The contrivance is this. If you will look at the edges 
of the eye-lids, you will see on each, near the end 
toward the nose, a very little opening. Into these 
openings, seen at c <?, in the Figure, the tears go, and 
pass through two ducts which unite in one, de. This 
ends in the nose. This sink-drain of the eye, as we 
may call it, is continually emptying its contents 
there. 

27. Sometimes this drain gets stopped up, and then 
the tears overflow their banks, the lids, and run down 
the cheeks. When one weeps, the tear factory makes 



Describe the tear apparatus ? What two purposes do the tears serve ? 
Why have fishes no tear-glands and no eye-lids? Describe the dr^in 
by which the tears are carried off. From what causes may the tears 
overflow the lids? 




166 FIRST BOOK IN PHYSIOLOGi. 

Fig. 69. ^ teai's SO fast that the drain cannot take 
them all away, and there is an overflow. 
There is a curious contrivance for carry- 
ing off the tears when the eyes are closed 
fi^'CCI in sleep. The lids close in such away 

as to leave a three-cornered canal be- 
tween them and the surface of the eye- 
ball, as represented in Fig. 69. In this 
diagram the line h is the surface of the front of the 
eye, and a points to the edges of the two lids. The 
little open space which you see shows you the form 
of the canal. It is through this canal that the tears 
flow, all the time that we are asleep, to the openings 
that lead into the sink-drain. 

28. There is still another contrivance, in regard to 
the tears, which I will notice. Along on the edge of 
each lid, among the roots of the eye -lashes, are some 
ittle glands that secrete an oily substance. This, 
besides oiling the eyelashes, serves to keep the tears 
in the eye. It makes an oily line all along the edge 
of the lid ; and, as water does not mix with oil, the 
tears will not pass over this line unless they are more 
abundant than usual. If it were not for this simple 
but effectual contrivance, the tears would be con- 
stantly diffused over the edges of the lids, and the lids 
would therefore be all the time wet. This would 
certainly be the case with the lower ones. 

29. Such is the wonderful apparatus of the human 

eye. It would be interesting now to show you how 

— ^. ^ 

What contrivaDce is there for carrying off the tears during sleep! 
Mention the contrivance for keeping the tears from moistening tlie out- 
Bi(^e of tlie eyehds. 



THE' EYE. 107 



tlie eyes of different kinds of animals vary from the 
human eye in their arrangements. I will speak, 
however, only of the compound eyes found in insects. 
They are made up of many eyes. Thus in the two 
eyes of the common fly there are eight thousand little 
eyes, as the microscope shows us. In some insects 
they amount to twenty thousand. Each of these is a 
tube, at the bottom of which an image can be formed, 
just as you have seen that there is on the retina of the 
human eye. Each of these eight thousand eyes in the 
fly sees perfectly of itself, having its own nerve of 
sight. The fly therefore can see in various directions, 
without turning its head, and it sometimes nses one 
part of this extensive optical apparatus and some- 
times another, according to tlie direction in which it 
wishes to look or the number of things it wishes 
to see. 

30. It has been found by the microscope that the 
little eye-tubes, of which the eyes of insects are made, 
are not always of the same shape. In some they are 
hexagonal or six-sided. This is the case with the eye 
of the yellow beetle, or May-bug. A magnified view 
of a small portion of the surface of this insect's eye is 
given in Fig. 70. In some butter- fig. 70. 

flies the little eyes are of a square 
ehape, as represented in Fig. 71. 
Why there should be this diflfer- 
ence in shape we know not. These 
compound eyes of insects are 






What is said of the eyes of insects? How many eyes has the com- 
mon fly ? How many hara some other insects? Are t'le <^yes of inseeta 
ill shaped alike? 



168 FIRST BOOK IN PHYSIOLOGY. 

among tbe most wonderful things ^^^- '^^• 

that the microscope has revealed to 
us. .We admire the skill and power 
of the Creator as we look at the con- 
struction of the human eye ; but His 
skill and power appear vastly more wonderful, when 
we think of the eye of a mere common insect, as made 
up of thousands of optical instruments, each, though 
so minute, being more perfect than any instruments 
^.hat man can make. 




CHA.PTER XI, 
THE EAR. 



1. The mind acquires the knowledge of sounds by 
the apparatus of hearing. This apparatus is very 
complicated, and some of it is exceedingly delicate. 
Before describing it I will say something of sound, in 
order that you may better understand the operation of 
this apparatus. 

2. Sound is caused by a vibration or shaking of 
some substance. You can perceive this vibration in a 
bell if you touch it after it has been struck. If the 
bell is quite large you can see as well as feel the 
vibration. You can see it in the string of a piano or a 
violin. It is the vibration of the cords in the larynx 
that produces the sound of the voice. It is not solid 
bodies alone that produce sound by their vibration. 

Why are the compound eyes of iusects more wonderful than the hu- 
foau eye ? How is sound pi^oduced ? Give examples of sound made by 
the vibration of lir ? 



^ 



THE EAR. lt>i^ 



It is often produced by the vibration of the air. This 
is the case in whistling. In the flute it is the vibra- 
tion of the air in the instrument that produces the 
sound. And so of other similar instruments. 

3. When the vibrations are equal, the sound is a 
musical one. But when they are irregular, the sound 
is a noise, that is, a confused sound. 

4r. Sound passes through the air by vibrations. It 
may be said to pass by waves in all directions, just as 
waves go in all directions on the surface of water 
when a stone is dropped into it. And as these waves 
in the water lessen as they extend from the spot where 
<ihey begin, so the waves of sound lessen the farther 
they are from where the sound is produced. That is, 
♦■Jie sound dies away in the distance, as it is expressed. 

5. That sound is transmitted in this way through 
the air can be proved by experiment. If a bell be 
^et to ringing under the glass receiver of an air-pumv> 
QS you pump the air out of the receiver, the sound < f 
the bell becomes more and more faint, till at leng ;h 
you cannot hear it at all. The reason is, that the vibra- 
tions of the air lessen as the air itself lessens and oe- 
comes thin ; and when the air is kill pumped out, 
there are no vibrations to convey the sound of the 
oell. So, too, sounds made on the top of a very high 
mountain are not as loud as when made in the valley 
oelow, because the air at so great a height is ver^* 
thin. 



What makes the difference between a musical sound aud a Loise 
How does sound pass through the air ? Give the comparisou in regard 
to the diffusion of sound. How can you prove that souud passes 
through air bj vibrations? 
ft 



ttO FIRST BOOK JN PHYSIOLOGY. 



6. Other substances besides air transmit the vibra- 
tions or motions of sound. If you put your head un- 
der water, and let some one stril{:e two stones together 
ander the water at some distance from you, you will 
hear the sound. Tliat is, the vibration will come to 
your ear through the water. If you place a watch 
between your teeth, you hear its ticking quite as dis- 
tinctly as when you put it to your ear. In this case 
the vibration goes to the nerve of hearing by the teeth 
and the bones, and does not go round by the air into 
the tube of the ear. 

7. The vibration of sound passes more readily 
through solids than through the air. If you put your 
ear upon the end of a long log you can hear the 
scratch of a pin made at the other end. And yet you 
cannot hear it through the air at the distance of only 
a few feet. A deaf gentleman, as he rested the bowl 
of his long pipe upon his daughter's piano, tound that 
he could hear the music much more distinctly tlian lie 
could through the air. In this case the vibration 
went through the pipe to the teeth, and then through 
the bone to the nerve of hearing. 

8. The vibrations or waves of sound are reflected 
by objects against which they strike. For this reas »n 
a sound can be heard further along a wall than in an 
oper; field. If one speaks in an open fleld, the sound 
is scattered in all directions. But the wall keeps it 
from being thus scattered. For the same reason, a 



lUustrate Uie fact that other substances besides air transmit the vi 
brations of sound What is said of the transmission of sound througi 
solids compared with its transmission through air? Ulustrnte in vari 
ou3 \vavs the reflection of sound. 



THE EAR. 1'71 



Speaker can be better heard in a building than in the 
open air. In this case the walls shut in the waves of 
sound. So, also, a speaker can be heard better when 
the ceiling is low^ than when it is very high. When 
the ceiling is high much of the sound of the voice Is 
lost in the space above. In a speaking-tube, even a 
whisper can be heard at a great distance, because the 
waves of sound are so shut in by the tube. 

9. In liearing, the waves of sound are caught by 
the outer ear, as it is called, and they go into the tube 
which you see there. The purpose of this outer ear is 
to collect these vibrations and direct them into this 
tube. It is well shaped on the whole for this purpose, 
but the ridges and prominences that you see on it do 
not render any assistance in this respect. They 
merely serve to make the ear a comely organ. Some 
animals have ears which answer much better in col 
lecting the waves of sound than the ear of man does, 
because they need them. Man could hear more 
easily if his ears were larger, and were shaped more 
like the open end of a trumpet, but such ill-looking 
appendages are not necessary in his case. Pie some- 
times assists the ear in collecting the vibrations of 
sound by putting his hand up behind it. Yery deaf 
persons often use an ear-trumpet. The broad trumpet- 
shaped end is turned towards the speaker, so as to 
r;atch the waves of sound and direct them into the 
mbe of the ear by the pipe of the instrument. 

10. The vibrations of sound in the air, entering the 

What is the purpose of the outer ear? What is sair] of its shape 
L id the irregularities on its surface? What is said of the eais of some 
ti imals ? In what wav is the ear sometimes assisted ( 



172 FIRST BOOK IN PHYSIOLOGY. 

tube of the ear, strike upon a drum at the end of the 
tube. This drum of the ear is a membrane fastened 
to the bone, just as the drum-head of a common drum 
is fastened to its wooden rim. The vibrations that 
thus enter this tube as they strike the drum make it. 
to vibrate. 

11. The vibration does not stop here. It is commu 
nicated to a chain of little bones on the other side of 
the drum. The farther one of this chain of bones 
rests on another membrane or drum. The vibration 
is therefore communicated to this second drum. And 
this drum covers an opening into some winding pas- 
sages in solid bone. These passages are filled with a 
fluid, and the vibration of the drum over the opening 
makes this fluid to vibrate or shake. 

12. The fine delicate fibres of the nerve of hearing 
are in the midst of the fluid in the winding passages. 
They feel the vibration of the fluid there, and an im- 
pression goes by them through the trunk of the nerve 
to the brain, and is received there by the mind. And 
this completes the process of hearing. These winding 
passages, w^here the nervous fibres are at their post 
ready to feel the vibrations that come there, are the 
real halls of audience^ as we may call them. I will 
now describe some of these parts more particularly. 

13. The little bones in the ear are four in number. 
They are connected together, and are commonly 
Bpoken of as a chain of bones. In Fig. 72 they are re- 



Upon what do tbe waves of sound entering the ear strike ? Tracei 
the tiansmlssior of the vibration inward from the drum of the ear 
Where are the fibres of the nerve of hearing, and how are Ihoy iilFected if 
Wliat completes the process of hearing ? 



THE EAR. 



173 



Fig. 72. 




presented separate and considerably magnified, so thai 
you can see their shape distinctly. They are named 
from their shapes. They are the hammer^ m/ the 
aiivil^ i ; the round bone, Oy the smallest bone in the 
body ; and the stirrup^ s. The 
long handle of the hammer, 
A, is fastened to the middle of 
the drum of the ear, and its 
blunt end fits on to the anvil. 
The little round bone is fixed 
between the slender end of 
the anvil and the top of the stirrup. And the bottom 
of the stirrup presses upon the second drum of the 
car. In Fig. 73 you have a repre- fig. 73. 

sentation of these bones, together with 
the drum of the ear. When the vibra- 
tion of sound comes to these bones, 
the hammer receives it first and it 
passes to the anvil, then to the little 
round bone, then to the stirrup, which communicates 
to the drum that is over the opening to the winding 
passages. 

14. In Fig. 73 is represented, much magnified, the 
ohape of the winding passages, which I have told you 
are in solid bone. The middle part of it, v^ is the 
vestibule^ or common hall of entrance to the passages. 
From this go out on the upper side the semi-circular 
canals^ a?, y^ ^, and on the lower side the passages of 
the cochlea^ Tc, At is the opening into the vestibule 




Describe the little bones of the ear. In what order does the vibra 
tiou of a eonnd pass through this chair of bones ? Describe the winding 
passages 



174 



FIKST BOOK IN PHYSIOLOGY, 



Fig 74. 




that is covered by the se 
cond drum. This drum, you 
will remember, is pressed 
upon by the stirrup-bone. 
At T is another opening, 
■which is also covered by a 
membrane or drum. The 
cochlea is called so because 
it is shaped like a snail's 
shell. It is most curiously 
arranged, having two spi- 
ral passages, each taking 
two turns and a half around 
tt pillar in the middle. This part of the ear represented 
in this figure is called the labyrinth, because the 
winding passages are so complicated. 

15. Having thus noticed the different parts of the 
apparatus of hearing, let us look at it altogether, as 
represented in a map of it in Fig. 75. At ah ci^ the 
external ear; at d is the entrance to the tube of the 
ear/; at g is the drum of the ear. At h is the cavity 
beyond the drum where the chain of bones is, the 
bones being left out that the arrangement of the appa 
ratus may be more clear to you. At Jc is a tube 
svhich comes from the back part of the throat to this 
cavity. If you shut your mouth and close the nostrils 
with your fingers, and then force the air strongly 
from your chest into the mouth, you can feel the air 
pass through this tube into the ear where the little 
bones are. At I is the vestibule of the labyrintli ; at 



Why are the winding passages called the labyrinth? Describe the 
various parts "^f the ear as represented in Fig. ^75. 



THE EAR. 



175 



Fio. 75. 




PI are the semi-rircnlar canals ; at 72/ is the cochlea : 
;^t is the trunk of the nerve of hearing as it goes to 
brancfc out in the labyrinth; and at ^ ^ is the bone in 
which the labyrinth is inclosed. 

16. I will now describe to you the process of hear- 
ing, tracing its successive steps by means of the map 
of the apparatus. The vibrations or waves of sound 
go into the tube of the ear, df^ and strike on the drum, 
^, making it to vibrate. This vibration is communi- 
cated to the chain of bones in the cavity, h. The 
last bone in vibrating shakes the little drum that co- 
vers the opening into the winding passages, I m n. 
This sends a vibration throughout the fluid in all these 

Trace the process of hearing in its successive steps od this map oi 
the apparatus 



176 FIRST BOOK IN PHYSIOLOGY 

passages. The nervous fibres scattered through this 
fluid feel the vibration, and the trunk of the nerve, o. 
passes on the impression to the mind in the brain. 

17. Observe that there are five different vibrations 
in succession before the nerve of the ear is reached- - 
the vibration of the air, in the tube of the ear,/ — ot 
the drum, g — of the chain of bones in the cavity, A~~ 
of the little drum over the opening into the winding 
passages — and lastly, of the fluid in these passages. 
Every time that a sound is heard, these vibrations fol- 
low each other, in the order that 1 have mentioned. 
It seems a long process, as it is described, but it takes 
but an instant. And in hearing one speak, how rap- 
idly does one vibration follow another, and yet how 
distinct the difi'erent vibrations are as one sound suc- 
ceeds another. The successive vibrations can be 
exceedingly rapid, and yet be entirely distinct. You 
can observe this in the rapid strokes of some kinds ot 
machinery. You can observe it also, as you strike as 
rapidly as you can with a stick upon anything. For 
every blow of the stick you have the succession of 
vibrations that I spoke of in the first part of this par- 
agraph. And you cannot strike fast enough to make 
the vibrations mingle together. 

18. I have described hearing as it commonly 
occurs. But, as I have already told you in § 6, sounds 
do not always go in through the tube of the ear. 
They sometimes get to the w^inding passages by 
another way; as for example, the sound of the watch 

How many different vibrations are there for every sound ? W^hat i.-^ 
said of the distinctness and rapidity of the vibrations as tliey= follow 
each other ? 



THE EAR. I'7'^ 

when placed between the teeth. In such a case, there 
are not so many changes in the vibration as when we 
hear in the common way. There are only three 
vibrations to follow each other for every sound, viz., 
the vibration of the teeth, that of the bones between 
the teeth and the winding passages of the ear, and 
that of the fluid in these passages. 

19. You see, then, by such cases that there can be 
hearing without using the drum of the ear or the 
chain of bones. Indeed these parts may be destroyed, 
•ind 3^et if the winding passages are not at all injured, 
the person can hear, though of course not as well as 
when the apparatus is all there. The winding pas- 
sages, the halls of audience, as I have called them, are 
then really the essential part of the apparatus. And 
so long as the vibration of sound can in any way reach 
the fluid in them, and shake it so that the fibres of the 
nerve shall feel it, there will be hearing. But if the 
fluid be in any way let out of these passages there 
will be no hearing, although the drum of the ear and 
the chain of bones may be in perfect order, and may 
vibrate reo-ularly to the sounds that come into the 
tube of the ear. The vibration in this case will stop 
at the stirrup-bone, and will not reach the nerve. 

20. This innermost and most important part of the 
apparatus is very securely guarded from injury. The 
winding passages are inclosed in the hardest bone in 
the body. It is so hard that it is called the petrous 
or rock-like bone. 



May sounds be heard in some other way than through ilie tube of 
the ear ? What is tJie most important part of the apparatus of hearing ? 
ExphiiL in full. H<av are the winding passages guarded from injury ? 
8* 



ITS FIRST BOOK IN PHYSIOLOGY. 

21. The outer passage into the ear is well guarded 
and in rather a singular way. Besides the hairs that 
are in the tube, which serve to catch particles that 
may fly in, there is also a waxy substance secreted 
there. And this substance, though it is so different 
from anytliing else in the body, is, like everything 
else, made from the blood. It is made by some very 
small glands situated in the lining of the tube. It is 
very bitter, and the odor of it serves to keep out small 
insects which might otherwise creep or fly in. It 
answers this purpose so well, that although the tube 
is always open, it is quite uncommon to have an insect 
get into the ear. And when one does, it becomes so 
enveloped in the wax tliat its struggles can do but lit- 
tle harm. Commonly the insect soon dies — perhaps, 
in part, from the bitter dose which he is obliged t(^ 
take. 

22. I have thus, in this and the previous chapter, 
treated quite fully of two of the senses. Of the other 
senses I have spoken incidentally in other parts of the 
book. The organs of the different senses differ from 
each other, as they are fitted to inform the mind of 
the different qualities of things around it. For exam- 
ple, the organ of smell is very different from the 
organ of hearing. Fine particles pass from bodies 
that give out an odor ; and these, coming in contact 
with the nerve spread out in the nose, make an im- 
pression, which is transmitted by the nerve to the 
brain. But in hearing, no particles from the sound 
'ug body come in contact v/ith the nerve. A mere 
ihaking or vibration goes tlirough the air to the. drum 

How is the tube of the ear guarded ? Give the difference stater^ 
^pt^reei/ the ors"an of siii'l] v.u(] tlmt of lieai'ino; ^ 



I HE EAR. 1'79 



of th(^ ear, and is passed on from tliis tlirongh the 
chain cf bones to the fluid that surrounds the iibres 
of the nerve of hearing. 

23. In the sense of taste^ the particles of the sub- 
stance tasted are commonly applied in a coarser way 
to the nerve than in the sense of smell. In the sense 
i)i touchy the substances do not, as in smell and taste, 
come into actual contact with the nerves. They are 
felt through the cuticle ; for this, as I have told you 
in § 28, Chapter VI., is not sensitive at all ; that is, 
it has no nerves, but is only a soft delicate covering 
to the very sensitive true-skin. 

24. In regard to the sense of sight^ we know not 
what it is that enters the eye and pictures the images 
of tilings on the retina. Light is now generally sup- 
posed to be a vibration of an exceedingly fine sub- 
stance, finer than air, which is thought to exist every- 
wdiere. The vibration of this substance, wdiich is 
called ether, is thought to be like the vibration of air 
in sound. Like that, it goes in weaves, in all direct 
tions, from where it begins. If light and sound are 
thus only motions, they are in some respects dif- 
ferent motions. They never interfere with each 
other, though they are continually mingled together, 
and cross each other in all directions. They difi*er in 
one respect very much. Light is a much faster vibra 
tion than sound. If you look at a cannon fired at a 
distance, the flash comes to your eye much sooner than 
the sound comes to your ear. The same is true also 
of the flash of lightning and its sound, the thunder. 

What is said of the sense of taste? What of the sense of touch? 
What is light supposed to be? What is said of the vibrations of 1i<rh( 
Hpd sound 2 ^ 



180 FIRST BOOK IN PHYSIOLOGY. 

CHAPTER XII. 
CONNECTION OF THE MIND AND BODY. 

I HAVE already said much of the connection of the 
mind and the body. I showed you in the chapter on 
the Nervous System that this connection is main- 
tained by means of tlie brain and the nerves. You 
there learned, that all the knowledge which the mind 
gets of the w^orld around it comes from the senses by 
means of the nerves ; and also that the only way in 
which the mind communicates its knowledge to others 
is by means of the nerves that excite the muscles to 
action. In the chapters following that on the Ner- 
vous System, we considered the instruments by which 
the brain and nerves operate in thus connecting the 
mind with the world around it. These instruments 
are the muscles and bones, and the organs of the 
senses, the eye, the ear, the nose, the mouth, and the 
skin. In this chapter I wish to carry you on a little 
farther, and show you more than I have yet done in 
regard ti the manner in which the mind uses these 
instrurcents by means of the nerves. 

2. Tae mind is connected with every part of the 
body. It therefore feels what is done to any part, 
and it can move the muscles everywhere by willing to 
have them moved. But the mind, though it is con 
nected with every part, is not in every part. If yon 
pinch your finger the mind feels it as readily as if it 

(xive tbe summaiy, in §1, of what has been ah^eady said in regard lo 
the eoDDection of the mind and the body. How do you know that the 
m'md is connected with ever}^ part of the body ? 



CONNECTION OF THE MIND AND BOD I. Ibi 

were itself in the finger. So, also, it can mo\ r tha 
tinger as easily as if it were really there among the 
muscles. But if the hand be palsied, feeling and me 
tion are gone in the part ; and yet the mind may bt 
active, and move other parts that are not palsied, and 
feel what is done to them. 

3. The mind, then, is not, as life is, all over tht 
body. It is in the brain. This is its central office 
the nerves being its communicating wires. We seem 
to know very early in life that the mind is in the 
brain. The child is conscious that he does his think- 
ing in his head. But besides this consciousness, we 
know some facts that prove that the mind resides in 
the brain. Thus, if a man be knocked down senseless 
by a blow on his head, the mind feels nothing, and 
can move no part, because the mind's organ, the brain, 
is so much affected by the blow. .He breathes still, 
and his heart beats, because the mind, as you saw in 
§83 in the chapter on the Muscles, does not contro 
these operations. If the blow break the skull, and the 
broken part be pressed in upon the brain, the man 
will not think, and feel, and move, until the surgeon 
remove the pressure by raising the broken piece. 

4. The brain is shown to be the organ of the mind 
by the manner in which the mind is affected by dis- 
ease in the brain. Fever causes delirium by disordering 
the brain, and a violent inflammation of the brain pro- 
duces fierce delirium. We sometimes see the mind 
blotted out, step by step, by slow disease in the brain. 

How do you know that the mind is not in every part? Whal is said 
of the consciou«*ness that the mind has its seat in the brain? Wliat 
tkct can you cite that proves that it has its seat there ? 



182 FIRST BOOK IN PHYSIOLOGY. 



SO that the strong-minded man becomes gradually like 
an idiot. 

5. You see, then, that the mind or soul, so long as 
it remains in the body, is dependent upon the brain 
It can act only hy means of this organ. If the brain 
be disordered in any way, the mind acts in a disordered 
inaimer. If the brain be much presr^ed upon, the 
mind cannot think, nor feel, nor move any part of the 
body. The mind is still there, bt.t it is torpid When 
the pressure is taken off, it comes out of this torpid 
state. 

6. As the brain is the organ with which the think- 
ing is done, we find that those animals that think 
much have larger brains than those that think but lit- 
tle. A frog thinks very little, and he has a small 
brain. An oyster thinks still less, and it would be 
hard to make out where his brain is. But such ani- 
mals as the canary-bird, the dog, and the horse, that 
know so much, have brains of considerable size. Man 
has a lai'ger brain in proportion to his body than any 
other animal, because he has to think so much more 
than other animals do. And men that think much 
lave larger brains than the stupid and ignorant. 

7. The mind in the infant is feeble, just like its 
body. It knows but little. But as the body grows. 
the mind grows also, and continually adds to its know- 
ledge. I wish to show you now how it does this. 

8. If you look at a very young infant, you will 
Bee that it does not know as yet how to use its mus 
cles at all w^ell. It moves its hands about awkwardly. 

How does disease sometimes show tliat the mind resides in the brain \ 
What is sail of the size of the brain in diflferent animals and in man 
What is sai 1 of the mind of the infant ? 



COJN.VECTION OF THE MIND AND BOD\ 183 



It cannot even hold any thing in them. It does 
not use its eyes well. It cannot turn them so as to 
look directly at any thing, but they roll about in 
their sockets irregularly. It doe? not see any thing 
clearly. 

9. The mind, you see, then, has to learn to use its 
instruments, the senses and the muscles. And the 
more it learns how to use them, the more knowledge 
it gets of the world around it. It learns, for example, 
to use the muscles and the nerves of touch, so as to 
know hard things from soft, rough from smooth, &c. 
In these ways it is continually learning more and 
more about the world of things with w^hich it is sur- 
rounded. 

10. In learning to use the senses, the mind makes 
one sense help another. Thus, the child sees a thing 
held before it, but as he reaches out his hands to touch 
it, it is plain that he does not know at first how far otf 
it is. But after a while, by touching it again and 
again, he knows w^here it is. That is, by his sense of 
touch he corrects the report which the sense of sight 
makes to his mind. He makes many such corrections 
every day, and after awhile becomes able generally to 
estimate at what distance objects are the moment he 
looks at them. Just so the infant has to learn to use 
its ears as well as its eyes. It knows nothing at first 
of the direction of sound, or of the distance from 
which it comes. 



What is said of the nse wbicb tlie infant makes of the miisclas and 
ibe senses? What is said of its learning to use tliem ? Illustrate the 
fa.*'A that the mind makes one sense help another in hai-uing to us^ \\\e 
Bfi'ses '< 



184 FIRST BOOK IN PHYSIOLOGY. 

11. It is a long training that the mind has to go 
through in learning to use the muscles. The hand of 
the infant is of little use at first, but after a time he 
learns to hold things in it. And from this the mind 
goes on to use the muscles of the hand more and 
more, till, in some cases, as in the skilful engraver or 
penman, it acquires wonderful skill in the movement 
of these muscles. The child learns to perform many 
different motions before he comes to try that very 
general motion of the muscles of the body, creeping. 
And then, in learning to walk, all the muscles that 
move the body, the head, the legs and the arms,' are 
exercised in balancing movements, day after day, for 
a long time, before he can acquire such skill in the 
use of the muscles as to walk off readily and with 
scarcely thinking of what he is doing. 

12. In learning to talk and sing, the mind learns 
how to use muscles, just as in learning to walk. These 
are nicer and more difficult operations, and so it takes 
the mind longer to learn them than to learn to use the 
muscles in walking. Especially is this true of learn- 
ing to sing. The mind is obliged to practice a long 
time on the muscles of the larynx, in order to use 
them skilfully in singing. 

13. In training the muscles of the voice in speaking 
and in singing, the ear acts as the teacher. It is only 
by the hearing that w^e know that we make the right 
sounds. When the child begins to talk, he makes 
vario^is trials of the sounds that he wishes to utter, his 

What is said of the time required for learning to use the nnuscles i 
What is said of learning to talk and sing ? Why does it take longer tc 
learn to do these than to learn to walk ? 



CONNECTION OF THE MIND AND BODY. 18a 

ear all tbo time listening, that his mind may know 
when he utters them correctly. So, when one is learn- 
ing to sing, the ear listens to inform the mind when 
the note is properly sounded. In learning both to 
talk and sing, the ear is thus continually correcting 
the mistakes which the mind makes in using the mus- 
cles of the voice. 

14. So necessary is the ear in the training of the 
muscles of the voice, that these muscles are never 
used in a child that is born deaf. In almost all the 
deaf and dumb there is no defect in the organs of the 
voice. The apparatus is all there — the articulating 
parts, the tongue, palate, (fee, the larynx with its vocal 
ligaments, and the muscles that tighten them, so that 
they may vibrate, and the muscles of the chest that 
force out the air to strike upon them. And the mind 
has its nerves running from the brain to all parts of 
the apparatus. But the mind does not w^ork the appara- 
tus, or play on the instrument, as we may say, simply 
because it has no guide in doing it. There being no 
hearing, the mind has no means of knowing when the 
right sound is uttered, and therefore it utters none. 
The deaf and dumb are dumb because they are deaf. 

15. If a child, instead of being born deaf, becomes 
deaf while it is learning to talk, he will remember the 
motions of the muscles of the voice by which he 
uttered some words, the names of common objects, 
such as hat, watch, &c. He can therefore pronounce 
these words, but he does it very awkwardly, because 
there is no hearing to guide the /oice. 

What acts as the teacher in learning to talk and '^^g^ Illustrate 
»:his. What is said of the deaf and dumb? What is sa- ^ f children 
Uiat Vecome deaf and duml^ while learning to talk ? 



iS6 FIRST BOOK IN PHYSIOLOGY. 

16. I have thus told you how the mind uses the 
muscles of the body. It is a very complicated ma- 
chinery that the mind works. There are over four 
hundred muscles in the body, and the mind works 
them by a multitude of nerves that go from the brain 
to them, 

17. Observe, now, that the mind in most cases 
knows nothing about all this machinery of the mus- 
cles. Your mind wills that your hand be raised, and 
it is instantly done. You may not know what muscles 
do this, and if you do you cannot perform the motion 
any better than if you did not know. The anatomist 
that knows the names of all the muscles, and under- 
stands how they are arranged, cannot use them any 
better than those who know nothing about this. The 
skilful balancer would not be any more skilful, if he 
had all the knowledge which the anatomist has. The 
famous singer could not sing any better if he should 
know how the little muscles in his throat work in pro- 
ducing the different notes. 

13. When man works any machinery that he has 
made, it is necessary tliat he should understand its 
various contrivances. Thus, the sailor cannot guide 
the ship unless he knows all about its rigging. But it 
is not so, as you have seen, with the macMnery that 
the mind works in the body. The mind does not 
look at the hundreds of muscles that it works, as the 
sailor looks at the various ropes with which he man- 



What is said of the musi ular macbineiy that the mind works ? How 
much does the miud know about this machinery? Could it work any 
better if it knew all about it ? Stat^ the comparison given in regard to 
machinery made by man. 



CONNECTION OF THE MIND AND BODY. 187 

ages his vessel. And when it wishes to perform any 
motion, it is not obliged to consider what muscles it 
must put into action. It simply wills that the motion 
shall be done, and instantly something, we know not 
what, goes along a multitude of nerves to a multitude 
jf muscular fibres, and they contract just enough to 
perform the motion. 

19. For every different motion a different message, 
as we may call it, is sent along the nerves. If you 
raise your hand, a message is sent through the nerves 
to the muscles that do it. Now, if you raise it again, 
but in a little different manner, a little lower or 
higher, or a little more to one or the other side, a lit- 
tle different message is sent along the nerves to those, 
muscles. And the same can be said of the muscles 
of any other part of the body. You see, then, that 
while any machinery made by man can perform bat 
a few motions, this machinery of the muscles can 
perform motions of any variety. 

20. I have already spoken of the variety of mo- 
tion that the muscular machinery can perform, in the 
chapter on the muscles, § 12 and § 13, and therefore 
will not dwell on it here. For all this variety there 
is a corresponding variety in the messages or impres- 
sions sent from the mind to the muscles. Even when 
the muscles only vary in the degree of their action, 
for every different degree there must be a different 
message. Thus, if in playing on a piano, you press 



What is said of tlie different motions perfornied by muscles ? lUus 
trate by referring to the hand. What is said of the great variety ol 
muscular aciion. Illustrate this variety as produced by varying the 
thgroi and tlip rU'^^ction of the action of mu5<^ies ? 



188 FIRST BOOK IN PHYSIOLOGY, 

on the same key twice in the same way, except that 
you vary the degree of pressure, tw^o different mes- 
sages are sent to the muscles that make the pressure, 
telling them in each case how hard to press. Much 
more, then, must the messages of the mind to the mus- 
cles vary, when their action is not only varied in de- 
gree, but in direotion also, as when the hand moves 
from one key to another in playing on the piano. 

21. In the chapter on the Muscles you saw that 
generally many muscles act together in producing 
any motion. For the different motions of any part, 
theUj there must be a vast variety of messages sent 
along the nerves of the muscles in that part. You can 
get some idea of this variety, if you move your hand 
about in as many different ways as you can think of, 
remembering what a number of muscles there is at 
work while you are doing this. 

22. In estimating the variety of the messages sent 
to the muscles, you are to remember that a separate 
message is sent to every fibre of a muscle by its little 
nervous tube, as mentioned in § 9, in the chapter on 
the Nervous System. How wonderful it is, that in 
all this multitude of messages that are sent to the 
fibres of the muscles, there should commonly be no 
mistake in any of them. In every motion each fibre 
gets its message correctly, and acts in obedience to it. 
Tou will realize how wonderful this is, if you turn 
back to the chapter on the Muscles, and read again 

What is said in §21 of the variety of messages sent by the nerves to 
the muscles of any part ? What are you to remember in estimati«g 
this variety ? ^^at is very wonderful in regard to this? 



CONNECTIOJM OF THE MIND AND BODY. 189 

all that I say there of the variety there is in ^he action 
of the muscles. 

23. When the muscles in different parts of the 
body are at work at the same time, in some general 
movement, the variety of messages that go to and 
from the brain is inconceivably great. When one is 
walking, for example, the mind continually sends a 
multitude of messages to all the muscles that together 
perform this general motion of the machinery. At the 
same time there are messages going to the brain from 
some of the organs of the senses, perhaps from all of 
them. But the variety in the messages is more strik- 
ing when different motions are performed in different 
parts of the body. Observe one who is playing on a 
parlor organ, and at the same time is singing. Mes- 
sages are sent in this case to many different parts for 
different purposes — to the muscles of the foot that work 
the bellows — to the muscles of the arm and hand and 
fingers in playing on the keys — to the muscles of the 
eyes in moving them to look at the notes — to the 
muscles of the vocal ligaments in making the different 
notes — to the muscles of the throat, lips, &c., in arti- 
culating the sounds — and to the muscles of the chest 
in forcing out the air through the windpipe. While 
all this is going on, the ear is listening to discover if 
there be any error in the sounds, the eyes are looking 
at the notes, and the sense of touch is guiding the 
muscles of the hand in regulating the degree of press- 
are on the keys of the organ. That is, while messages 

What is said of the variety of messages that go along (he nerves 
when one is walking? In what cases is this variety most striking if 
f+ive the illustration. 



1^0 FIRST BOOK IN PHYSIOLOGY. 



are going from the mind with such rapidity and va- 
riety to the muscles of the foot, the hands, the eyes, 
the throat and the chest, messages are coming to the 
mind from the ears, tlie eyes and the fingers. The 
communications of the mind with the different parts 
of the body are in such a case numerous and compli- 
cated beyond conception. 

24. I have thus shown you how the mind makes 
use of its instruments, the organs of the senses and 
the muscles. I have spoken of them as the machinery 
of the mind, and you have seen that these instruments 
contain mechanisms that are more perfect and beauti- 
ful than any that man ever constructed. Yoa have 
seen that the body is mostly a collection of machinery 
for the mind to use, and that the purpose of those 
parts which the mind does not use is to build those 
w^hich it does use. The object of one portion of the 
machinery of the mind, the organs of the senses, is, as 
you have seen, to enable it to gain a knowledge of the 
world around it. The object of the other portion of its 
machinery, the muscles, with the parts that they 
move, is to use this know^ledge gained by the senses in 
making impressions upon the things and beings with 
which it is surrounded. It works w^ith the muscles, 
and with them communicates its knowledge to others. 

25. This machinery of the mind is fitted for ouf 
present state of being. But this life is short. This 
body, with all its ingenious and beautiful contrivances, 
is to be dwelt in and used by the mind but a short 
period of time. In the life which follows, its evei- 

Give the summary in §24. What is said of the instrmnents whicK 
the mind will use ia anothei* life? 



CONNECTION OF THE MIND AND BODY. 191 

lasting life, it is to have, as the Bible tells us, a better, 
a glorified body. It will, therefore, have better in- 
Rtruments to use then than it has now, and so will be 
able both to know more and to do more than it cars 
in its present state. 



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